IBA MDCAT Reconduct Test, held on 8 December 2024

Correct Answer: D. Brain Cells

In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as helper T cells, monocytes, macrophages, and dendritic cells.

Correct Answer: B. Hepatitis B

The correct answer is B. Hepatitis B.
Hepatitis B is a reverse transcribing diploid single-stranded RNA virus. It belongs to the Hepadnaviridae family and has a unique replication cycle that involves reverse transcription of its RNA genome into DNA.

Correct Answer: C. Viruses

The correct answer is C. Viruses.
The Russian scientist referred to is Dmitri Ivanovsky. In 1892, he conducted experiments with tobacco plants and discovered that the agent causing the tobacco mosaic disease could pass through filters fine enough to block bacteria. This marked the discovery of viruses, which are much smaller than bacteria and capable of passing through such filters.
Ivanovsky’s work laid the foundation for the study of virology, although it was later confirmed and expanded upon by others, such as Martinus Beijerinck.

Correct Answer: B. They cause infections, and can only replicate inside living cells

The correct answer is:
B. They cause infections, and can only replicate inside living cells.
Explanation:
Viruses are non-cellular infectious entities because they lack a cellular structure (no nucleus, cytoplasm, or organelles) and are not considered alive outside of a host organism.
They are obligate intracellular parasites, meaning they cannot replicate or carry out metabolic processes outside of a living host cell. Once inside a host cell, they hijack the cell’s machinery to produce more virus particles.

Correct Answer: D. The molecule that releases energy when the phosphate molecule is removed

The correct answer is:
D. The molecule that releases energy when the phosphate molecule is removed.
Explanation:
ATP (adenosine triphosphate) is the primary energy currency of the cell.
It consists of three phosphate groups, and energy is stored in the high-energy bonds between these groups.
When a phosphate group is removed (via hydrolysis), ATP is converted to ADP (adenosine diphosphate) or AMP (adenosine monophosphate), and energy is released. This energy powers various cellular processes, including muscle contraction, active transport, and biosynthesis.

Correct Answer: C. 4 ATP are produced and 2 ATP are consumed

The correct answer is:
C. 4 ATP are produced and 2 ATP are consumed.
Explanation:
Glycolysis is the process of breaking down one molecule of glucose into two molecules of pyruvate, which occurs in the cytoplasm.
During glycolysis:
2 ATP molecules are consumed in the energy investment phase.
4 ATP molecules are produced in the energy payoff phase.
The net gain of ATP is 2 ATP per glucose molecule.

Correct Answer: C. 2H, 2e and 1/2O2

The correct answer is:
C. 2H, 2e, and 1/2 O₂
Explanation:
During the light-dependent phase of photosynthesis:
Photolysis of water occurs, which is the splitting of water molecules into their components using light energy.
The reaction is:
2H2O→4H++4e−+O2
For one molecule of water:
H2O→2H+ +2e− +1/2 O2
Thus, for every water molecule broken down:
2 protons (H⁺) are released.
2 electrons (e⁻) are released.
1/2 molecule of oxygen (O₂) is produced.

Correct Answer: D. Tetrose

The correct answer is:
D. Tetrose.
Explanation:
Erythrose is a monosaccharide with the chemical formula C₄H₈O₄.
It contains four carbon atoms, classifying it as a tetrose.
Specifically, erythrose is an aldose sugar (an aldotetrose) because it has an aldehyde group.

Correct Answer: A. Oxygen

The correct answer is:
A. Oxygen
Explanation:
In the Electron Transport Chain (ETC), oxygen serves as the ultimate (final) electron acceptor. Here’s how it works:
Electrons are passed along a series of protein complexes and coenzymes embedded in the inner mitochondrial membrane.
As electrons move through the chain, they release energy, which is used to pump protons (H⁺) across the membrane, creating a proton gradient.
At the end of the chain, electrons are transferred to oxygen, which combines with protons to form water: O2+4e^−+4H^+→2H2O

Correct Answer: A. Pyrogen

The correct answer is:
A. Pyrogen
Explanation:
The hypothalamus is a critical brain region involved in regulating body temperature, among many other functions. It produces and responds to signaling molecules called pyrogens in response to infections or inflammation. Pyrogens, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF), signal the hypothalamus to increase the body’s set-point temperature, leading to fever. The hypothalamus produces or responds to pyrogens, which are signaling molecules involved in regulating fever and immune responses.

Correct Answer: D. Alpha-1, Beta-2

he correct answer is:
D. Alpha-1, Beta-2
Explanation:
Glucose and fructose are linked together in sucrose through a glycosidic bond.
The glycosidic linkage forms between the anomeric carbon (C-1) of glucose (in the alpha configuration) and the anomeric carbon (C-2) of fructose (in the beta configuration).
This linkage is specifically referred to as an alpha-1, beta-2 glycosidic bond.

Correct Answer: A. Syphilis

The correct answer is:
A. Syphilis
Explanation:
Syphilis is a bacterial infection caused by the bacterium Treponema pallidum, not a viral disease.
The other options are all viral diseases:
B. AIDS: Caused by the HIV virus (Human Immunodeficiency Virus).
C. Hepatitis: Caused by several viruses, including Hepatitis A, B, C, D, and E.
D. Polio: Caused by the poliovirus.
Summary:
Syphilis is the exception because it is a bacterial disease, while the others are viral infections.

Correct Answer: A. High Light Intensity

The correct answer is:
A. High Light Intensity
Explanation:
Cyclic phosphorylation is a process in photosynthesis that occurs in the light-dependent reactions. It involves the cyclic flow of electrons through photosystem I (PSI) and the electron transport chain, leading to the production of ATP but not NADPH.
It is typically stimulated by high light intensity, which increases the rate of electron flow through PSI, favoring cyclic phosphorylation over linear electron flow.

Correct Answer: B. Hydrophobic Exclusion

The correct answer is:
B. Hydrophobic Exclusion
Explanation:
Hydrophobic exclusion is a key property of water that plays a crucial role in biological membrane stability. This refers to the tendency of water molecules to exclude nonpolar (hydrophobic) substances, forcing them to aggregate in the interior of biological membranes. This helps to maintain the structure of lipid bilayers, which are essential for the function of cell membranes.
In biological membranes, the hydrophobic (water-repelling) tails of phospholipids face inward, away from the water, while the hydrophilic (water-attracting) heads face outward toward the water. This arrangement is stabilized by the hydrophobic exclusion effect.

Correct Answer: B. Acylglycerol

The correct answer is:
B. Acylglycerol
Explanation:
Acylglycerol (also known as triacylglycerol or triglyceride) is a compound formed when one glycerol molecule is esterified (linked) with three fatty acids.
This process is called esterification, where each fatty acid is joined to the glycerol molecule through an ester bond.

Correct Answer: C. Physical Activity

The correct answer is:
C. Physical Activity
Explanation:
Pulmonary volume refers to the amount of air that the lungs can hold during different phases of the respiratory cycle, including tidal volume, inspiratory reserve volume, and expiratory reserve volume.
Physical activity significantly influences pulmonary volume because during exercise or exertion:
Tidal volume (air inhaled/exhaled per breath) increases to meet the body’s higher oxygen demands.
Inspiratory and expiratory efforts become more pronounced, utilizing more lung capacity.

Correct Answer: C. Middle lamella

The correct answer is:
C. Middle lamella
Explanation:
During cytokinesis in plant cells, the cell plate forms between the dividing cells. This cell plate eventually develops into the middle lamella, which is the first layer of the cell wall to form.
The middle lamella is primarily composed of pectins, which act as a glue to hold adjacent cells together.

Correct Answer: D. The cerebral cortex of the human brain is more developed

The correct answer is:
D. The cerebral cortex of the human brain is more developed
Explanation:
The cerebral cortex is a key feature of the brain responsible for higher cognitive functions, such as reasoning, language, decision-making, and problem-solving.
While animals also possess a cerebral cortex, it is more developed in humans, making humans capable of advanced intellectual and social behaviors.
The size and complexity of the human cerebral cortex, including its folds (gyri and sulci), allow for greater surface area and more neural connections compared to most animals.

Correct Answer: A. Peroxisome

The correct answer is:
A. Peroxisome
Explanation:
During photorespiration, which occurs when the enzyme RuBisCO fixes oxygen instead of carbon dioxide, glycolate is produced.
The glycolate is then converted into glycine in the peroxisome, which is one of the organelles involved in the metabolic processes of photorespiration.
This conversion involves a series of reactions where glycolate is first converted into glycine, and then glycine is processed further in the mitochondria.

Correct Answer: D. Proteins

The correct answer is:
D. Proteins
Explanation:
The selective permeability of the cell membrane is primarily due to the presence of proteins embedded in the lipid bilayer. These membrane proteins function as channels, carriers, or pumps to allow specific substances to pass through the membrane, while blocking others.
Transport proteins play a crucial role in regulating the movement of ions, nutrients, and waste products across the membrane.

Correct Answer: B. Hippocampus

The correct answer is:
B. Hippocampus
Explanation:
The hippocampus is a key part of the brain involved in the formation and consolidation of long-term memory. It plays a crucial role in converting short-term memories into long-term memories and is especially important for spatial memory and the recall of facts and events.

Correct Answer: C. Calcium Channel

The correct answer is:
C. Calcium Channel
Explanation:
When a nerve impulse (action potential) reaches the axon terminal, it causes the opening of calcium channels.
The influx of calcium ions (Ca²⁺) into the axon terminal triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft, which then propagate the signal to the next neuron or target cell.
The opening of calcium channels at the axon terminal is crucial for the release of neurotransmitters, which allows the transmission of the nerve impulse to the next neuron.

Correct Answer: C. Dendrites

The correct answer is:
C. Dendrites
Explanation:
Dendrites are the branched extensions of a neuron that receive stimuli (signals) from other neurons or sensory receptors. They then conduct the electrical impulse towards the cell body of the neuron, where the signal can be processed.

Correct Answer: D. 62

The correct answer is:
D.62 nerves
Explanation:
There are 31 pairs of spinal nerves that originate from the spinal cord. These 31 pairs are divided into:
8 cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral nerves
1 coccygeal nerve
Thus, the total number of spinal nerves is 62 (31 pairs). in standard anatomical terms, 62 is more accurate.
There are 62 spinal nerves that originate from the spinal cord, corresponding to 31 pairs.

Correct Answer: A. Protein

The correct answer is:
A. Protein
Explanation:
A disulfide bridge (or disulfide bond) is a strong covalent bond formed between the sulfur atoms of two cysteine amino acids in a protein. This bond helps stabilize the tertiary and quaternary structure of proteins, contributing to their overall shape and function.

Correct Answer: B. 3-phosphoglyceraldehyde

The correct answer is:
B. 3-phosphoglyceraldehyde
Explanation:
During the light-independent reactions (also known as the Calvin cycle) of photosynthesis, the first stable product formed with three carbon atoms is 3-phosphoglyceraldehyde (PGAL), also known as glyceraldehyde-3-phosphate (G3P).
PGAL is formed through the reduction of 3-phosphoglyceric acid (3-PGA), which is initially produced in the cycle.

Correct Answer: C. They kill the prey with the help of stinging cells

The correct answer is:
C. They kill the prey with the help of stinging cells
Explanation:
Cnidarians, such as jellyfish, sea anemones, and corals, use specialized cells called cnidocytes that contain nematocysts (stinging organelles). When these cells come into contact with prey, the nematocysts fire tiny, barbed threads that deliver venom to immobilize or kill the prey.

Correct Answer: A. Apoplastic Pathway

The Casparian strip blocks the apoplastic pathway, which involves the movement of water and minerals through the cell walls and intercellular spaces. The Casparian strip forces water and minerals to enter the cells (via the symplastic pathway) to regulate their entry into the vascular system.

Correct Answer: C. Liver Fluke

The correct answer is:
C. Liver Fluke
Explanation:
The liver fluke (Fasciola hepatica) completes its life cycle in two hosts: an intermediate host (usually a snail) and a definitive host (usually a sheep or man). The life cycle involves a complex series of developmental stages, including larvae that hatch in the water and infect snails, and then move to the liver of the definitive host where they mature and reproduce.

Correct Answer: C. It has excitatory effects on acetylcholine receptors

The correct answer is:
C. It has excitatory effects on acetylcholine receptors
Explanation:
Nicotine stimulates the sympathetic nervous system, leading to an increase in heart rate, blood pressure, and muscular activity. It does this by binding to nicotinic acetylcholine receptors, which are found in the autonomic nervous system. This binding activates the receptors, resulting in the release of neurotransmitters like norepinephrine that stimulate various body functions.

Correct Answer: A. Mesoglea fibrous, Polpoida forms only

The correct answer is: A. Mesoglea fibrous, polypoid forms only.
Explanation:
Class Anthozoa is part of the phylum Cnidaria and includes organisms like corals, sea anemones, and sea pens. Key characteristics of Anthozoa are:
Polypoid forms only: Unlike other cnidarians, Anthozoans do not have a medusa stage in their life cycle.
Mesoglea fibrous: The mesoglea (the jelly-like layer between the epidermis and gastrodermis) is typically fibrous and can have embedded cells, but Anthozoa is primarily known for its fibrous nature.
Marine habitat: They are exclusively marine organisms.
Radial symmetry: Most exhibit radial or biradial symmetry.
Option B, C, and D are incorrect as they include medusa stages or misrepresent the characteristics of the mesoglea.

Correct Answer: B. Enzyme molecules each have distinct shape

The correct answer is: B. Enzyme molecules each have distinct shape.
Explanation:
The lock and key hypothesis suggests that each enzyme has a specific active site that perfectly matches the shape of its substrate, similar to how a key fits into a specific lock. This specificity is due to the unique three-dimensional shape of the enzyme molecule.

Correct Answer: B. 1 & 3

The correct answer is:
B. 1 & 3
Explanation:
Hirudinaria (a genus of leeches) belongs to the class Hirudinea under the phylum Annelida. Common characteristics include:
Setae and parapodia absent: Leeches lack setae (bristle-like structures) and parapodia (fleshy lobes used for locomotion in some annelids).
Blood suckers are present: Leeches are equipped with anterior and posterior suckers for attachment and blood-sucking in parasitic species.
Hence, statements 1 and 3 are correct.

Correct Answer: A. Taenia

The correct answer is:
A. Taenia
Explanation:
Taenia: A genus of parasitic flatworms (tapeworms) that live in the intestines of humans as endoparasites. Common species include Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm).
Dugesia: A free-living flatworm, not a parasite, often found in freshwater.
Fasciola: A liver fluke, which is an endoparasite but primarily infects the liver of herbivorous animals and sometimes humans.
Hydra: A non-parasitic, freshwater cnidarian.
Thus, the flatworm that is an endoparasite of humans is Taenia.

Correct Answer: C. Competitive Inhibitor

The correct answer is:
C. Competitive inhibitor
Explanation:
Penicillin is an antibiotic that works by acting as a competitive inhibitor of the enzyme transpeptidase. This enzyme is essential for bacterial cell wall synthesis, as it catalyzes the cross-linking of peptidoglycan chains. By binding to the active site of transpeptidase, penicillin prevents the enzyme from functioning properly, leading to the weakening and eventual lysis of bacterial cells.

Correct Answer: B. 2% 

Oxygen is poorly soluble in plasma, so that less than 2 percent of oxygen is transported dissolved in plasma. The vast majority of oxygen is bound to hemoglobin, a protein contained within red cells. Hemoglobin is composed of four iron-containing ring structures (hemes) chemically bonded to a large protein (globin).

Correct Answer: B. Lamarck

The correct answer is:
B. Lamarck
Explanation:
The use and disuse theory was proposed by Jean-Baptiste Lamarck, a French naturalist. According to Lamarck’s theory of evolution:
Organs or traits that are frequently used become stronger and more developed over time.
Organs or traits that are not used gradually diminish and may disappear in subsequent generations.
This concept was central to his idea of inheritance of acquired characteristics, which is now largely discredited in light of modern genetics and Darwinian natural selection.

Correct Answer: D. Theory of special creation

The correct answer is:
D. Theory of Special Creation
Explanation:
The Theory of Special Creation states that all living entities were created by a divine power (God) in their current form, as described in various religious and spiritual texts. According to this theory:
Species were individually created.
They do not evolve or change over time.
Life exists as it was originally created.
This theory is rooted in religious beliefs rather than scientific principles and is distinct from evolutionary theories like natural selection or Lamarckian inheritance.

Correct Answer: D. Knee Jerk

The correct answer is:
D. Knee jerk
Explanation:
Polysynaptic transmission involves multiple synapses between neurons. Most complex actions, like breathing, playing a game, and heart regulation, involve polysynaptic pathways because they require integration of information.
The knee jerk reflex, however, is an example of a monosynaptic reflex arc, meaning it involves only one synapse between a sensory neuron and a motor neuron. This allows for a rapid, automatic response without involving the brain.

Correct Answer: D. SA node – AV node – Bundle of His – Purkinje

The correct answer is:
D. SA node – AV node – Bundle of His – Purkinje fibers
Explanation:
The correct sequence of impulse transmission in the human heart ensures coordinated contraction and efficient blood pumping:
SA Node (Sinoatrial Node): The natural pacemaker of the heart generates electrical impulses.
AV Node (Atrioventricular Node): Receives the impulse from the SA node and delays it slightly to allow the atria to contract fully.
Bundle of His: The impulse travels from the AV node to the ventricles via this specialized conduction pathway.
Purkinje Fibers: These fibers distribute the electrical impulse throughout the ventricles, causing them to contract.
This sequence is critical for the synchronized contraction of the heart chambers.

Correct Answer: C. T lymphocytes

The correct answer is:
C. T lymphocytes
Explanation:
B lymphocytes (B cells): These are responsible for producing and secreting antibodies in response to pathogens.
T lymphocytes (T cells): These cells do not secrete antibodies. Instead, they are involved in cell-mediated immunity, such as directly attacking infected or cancerous cells or regulating immune responses.
T Helper cells (a subset of T lymphocytes): They help B cells in antibody production by secreting cytokines but do not produce antibodies themselves.
U Helper cells: This seems to be a non-standard term and might be a distractor. It is not recognized in immunology.
Thus, T lymphocytes are the correct answer because they play a distinct role in immunity and do not secrete antibodies.

Correct Answer: B. Hyoid Bone

The correct answer is:
B. Hyoid Bone
Explanation:
The hyoid bone is a U-shaped bone located in the neck, between the lower jaw (mandible) and the larynx. It serves as an anchoring structure for the tongue and is considered to lie at the junction between the skull and the postcranial skeleton. It is unique in that it does not articulate directly with any other bones, being supported by muscles and ligaments.

Correct Answer: C. Neutrophils

The correct answer is:
C. Neutrophils
Explanation:
Neutrophils are the most abundant type of white blood cells (WBCs) in the human body, comprising about 60–70% of the total WBC count.
They are the first responders to sites of infection or injury, rapidly migrating to the area via chemotaxis.
Their primary role is to engulf and destroy pathogens, particularly bacteria, through a process called phagocytosis.

Correct Answer: B. T cells

The correct answer is:
B. T Cells
Explanation:
Non-specific immune responses are part of the innate immune system, which provides general defense mechanisms against pathogens without targeting specific invaders. Examples include:
Spermine: Found in semen, it has antimicrobial properties.
HCL (Hydrochloric Acid): Present in the stomach, it kills many ingested pathogens.
Mucus: Traps pathogens and prevents them from entering deeper tissues.
T Cells, on the other hand, are part of the specific (adaptive) immune response. They recognize and respond to specific antigens and play a critical role in cell-mediated immunity.
Thus, T Cells are not a non-specific immune response.

Correct Answer: D. Dionaea muscipula

The correct answer is:
D. Dionaea muscipula
Explanation:
Dionaea muscipula, commonly known as the Venus flytrap, is a well-known carnivorous plant that traps and digests insects and other small prey to supplement its nutrient intake. It is a classic example of a carnivorous plant.
Pinus geradiana: This is a gymnosperm (a pine tree) and not carnivorous.
Funaria hygrometrica: This is a moss and is non-carnivorous.
Polypodium glycyrrhiza: This is a type of fern and is also non-carnivorous.

Correct Answer: C. Lymphatic System

The correct answer is:
C. Lymphatic System
Explanation:
The lymphatic system is responsible for draining excess fluid (lymph) from tissues and returning it to the circulatory system (cardiovascular system). It plays a crucial role in maintaining fluid balance and also supports the immune system by transporting lymph, which contains white blood cells.

Correct Answer: D. Endodermis layer

The correct answer is:
D. Endodermis layer
Explanation:
The Casparian strip is a band of cell wall material found in the cells of the endodermis in roots. It is composed of suberin and lignin, which are impermeable to water and solutes. The Casparian strip plays a crucial role in regulating the flow of water and nutrients into the vascular tissue (xylem and phloem) by forcing them to pass through the selectively permeable plasma membrane of the endodermal cells. The Casparian strip is unique to the endodermis, ensuring controlled uptake of substances into the plant’s vascular system.

Correct Answer: C. Diaphram

The correct answer is:
C. Diaphragm
Explanation:
The diaphragm is a dome-shaped sheet of skeletal muscle that separates the thoracic cavity (containing the lungs and heart) from the abdominal cavity (containing the stomach, intestines, and other organs). It plays a crucial role in respiration by contracting and relaxing to facilitate breathing. The diaphragm is both a structural and functional boundary between the thoracic and abdominal regions.

Correct Answer: B. 1.204 x 10^23

Correct Answer: B. 1.66 x 10^-24 kg

Correct Answer: C. 100

Correct Answer: B. 1 atm

Correct Answer: B. Charles Law

Correct Answer: B. Mean free path

The mean free path is the average distance that a gas molecule travels between successive collisions with other molecules. It is an important concept in the kinetic theory of gases and depends on factors like the temperature, pressure, and size of the molecules.

Correct Answer: C. -3, -2, -1, 0, +1, +2, +3

Correct Answer: B. Zero

Correct Answer: D. If the particle moving across the field lines

The correct answer is:
D. If the particle is moving across the field lines.
Here’s why:
A magnetic field exerts a force on a charged particle only if the particle is moving.
The force on the particle is described by the Lorentz force law: F=q(v×B\times where:
q is the charge,
v is the velocity of the particle, and
B is the magnetic field.
For the magnetic force to be nonzero, the particle must be moving across the magnetic field lines (i.e., the velocity vector v is not parallel to the magnetic field B).
If the particle is at rest (option A), there is no force because velocity v=0.
If the particle is moving along the field lines (option B), the velocity vector is parallel to the magnetic field, and thus there is no force, because the cross product v×B is zero.
In general, the force always depends on the direction of motion relative to the magnetic field, and it’s only nonzero when the particle moves perpendicular (or at an angle) to the field lines.
Therefore, option D is the correct one.

Correct Answer: A. 1000V

Correct Answer: A. Ultraviolet Radiation

The correct answer is:
A. Ultraviolet radiation.
Skin cancer is primarily caused by ultraviolet (UV) radiation from the sun or artificial sources like tanning beds. UV radiation damages the DNA in skin cells, which can lead to mutations and the development of skin cancer, including melanoma, basal cell carcinoma, and squamous cell carcinoma.

Correct Answer: D. Rectification

The correct answer is:
D. Rectification
Explanation:
Rectification is the process of converting an alternating current (AC) waveform into a direct current (DC) waveform. This is typically done using devices like diodes, which allow current to flow only in one direction.
There are two main types of rectification:
Half-wave rectification: Converts only one half of the AC waveform into DC.
Full-wave rectification: Converts both halves of the AC waveform into DC.
Rectification is a key step in power supply circuits to provide DC voltage to electronic devices.

Correct Answer: A. Special theory of relativity

The correct answer is:
A. Special theory of relativity
Explanation:
This statement is one of the two fundamental postulates of Albert Einstein’s Special Theory of Relativity. The two postulates are:
The laws of physics are the same in all inertial frames of reference.
The speed of light in a vacuum is constant (approximately 3×10^8 m/s and is the same for all observers, regardless of the motion of the light source or the observer.
This principle leads to profound consequences, such as time dilation and length contraction, which are cornerstones of the special theory of relativity.

Correct Answer: B. 6.63 x 10^-16

Correct Answer: D. 2.5 gm

To solve this, we use the formula for radioactive decay:
mt=m0×(21)Tt
Where:
mt = mass remaining after time t.
m0 = initial mass.
T = half-life.
t = time elapsed.

Given:
m0=40
T=20days,
t=80days.
tep-by-Step Calculation:
Determine the number of half-lives that have passed:
Number of half-lives = t/T = 80/20 = 4
Apply the formula:
mt=40 ×(2/1)4 =40×1/16 = 2.5gm

Correct Answer: D. No change

When a nucleus emits two negative beta particles (β⁻ decay), the mass number remains unchanged because beta decay involves the transformation of a neutron into a proton, emitting an electron (β⁻) and an antineutrino in the process.
Key Points:
In beta decay:
A neutron (nnn) transforms into a proton (p):
en→p+β−+νˉe
The number of neutrons decreases by 1, and the number of protons increases by 1 for each beta decay.
The mass number (A) is the sum of protons and neutrons. Since one neutron is replaced by one proton, the mass number remains constant.
However, the atomic number (Z) increases by 1 for each beta decay, meaning it increases by 2 after emitting two beta particles.
Correct Answer: D. No change

Correct Answer: B. Strong Nuclear Force

The correct answer is:
B. Strong Nuclear Force
Explanation:
Strong Nuclear Force:
It is the force responsible for binding protons and neutrons (nucleons) together in the nucleus.
It is the strongest of the four fundamental forces but acts only over very short ranges 10−15 meters, the size of a nucleus).
It overcomes the repulsive Coulomb force between positively charged protons to keep the nucleus stable.
Other Forces:
Weak Nuclear Force: Responsible for radioactive decay and processes like beta decay but does not bind nucleons.
Coulomb’s Force: A repulsive force between positively charged protons, which the strong nuclear force overcomes.
Newton Force: Refers to gravitational force, which is negligible at the scale of the nucleus due to the tiny masses involved.

Correct Answer: B. Gamma Rays

The correct answer is:
B. Gamma Rays
Explanation:
Gamma Rays:
Gamma rays are high-energy electromagnetic radiation with no mass or charge.
They have the highest penetrating power among all types of radiation because they interact weakly with matter.
Thick lead or concrete is required to significantly reduce their intensity.
Other Radiations:
Alpha Rays: These are helium nuclei (2 protons and 2 neutrons). They have a low penetrating power and can be stopped by a sheet of paper or even skin.
Beta Rays: These are high-energy electrons or positrons. They have moderate penetrating power and can be stopped by materials like aluminum or plastic.
Proton Rays: Protons have greater mass than electrons and are charged particles. Their penetrating power is lower than gamma rays and depends on their energy.
Summary:
Gamma rays have the highest penetrating power due to their electromagnetic nature and high energy.

Correct Answer: A. 90m

Correct Answer: B. Coulomb

The correct answer is:
B. Coulomb
Explanation:
Electric Charge:
Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric field.
The SI unit of electric charge is the Coulomb (C).

Correct Answer: A. Faraday’s law of electromagnetic induction

The correct answer is:
A. Faraday’s Law of Electromagnetic Induction
Explanation:
Faraday’s Law of Electromagnetic Induction:
This law states that the electromotive force (emf) induced in a closed circuit is directly proportional to the rate of change of magnetic flux through the circuit.
Mathematically:
emf= − dΦB/ dt
where ΦB is the magnetic flux.

Correct Answer: C. 2Hz

Correct Answer: A. In, For

The correct answer is:
A. In, for
Explanation:
“Believed in”: The correct preposition to use with “believed” when referring to confidence in someone’s abilities is “in”.
“Ask for”: The correct preposition to use with “ask” when referring to requesting help is “for”.
Complete Sentence:
“Since she believed in her abilities, she didn’t ask for any help.”

Correct Answer: D. My bed is bigger than my desk

The correct answer is:
D. My bed is bigger than my desk
Explanation:
Rules for Comparative Degree:
To compare two things, the comparative form of the adjective is used.
For most one-syllable adjectives, add -er (e.g., big → bigger).
Use than to indicate the comparison (e.g., “bigger than”).
Why the Other Options Are Incorrect:
A: Incorrect spelling of “than” as “then.”
B: “More bigger” is grammatically incorrect because bigger already implies comparison.
C: “More big” is incorrect; the correct comparative form is “bigger.”
Correct Sentence:
“My bed is bigger than my desk.”

Correct Answer: B. There was heavy fog in the morning: the services at the airport were closed.

The correct answer is:
B. There was heavy fog in the morning: the services at the airport were closed.
Explanation:
The colon (:) is used to introduce an explanation, example, or result. In this case, the second part of the sentence explains the consequence of the heavy fog.
Correct Punctuation:
“There was heavy fog in the morning: the services at the airport were closed.”

Correct Answer: D. Extinguish

The correct answer is:
D. Extinguish
Explanation:
“Out out the fire” means to put out the fire, which refers to extinguishing or stopping the fire.
The word extinguish is the closest in meaning, as it means to put an end to a fire or to stop it from burning.
Correct Meaning:
“Extinguish” means to put out the fire.

Correct Answer: C. Grievous

The correct answer is:
C. Grievous
Short Explanation:
Grievous is the correct spelling and refers to something that causes serious pain, suffering, or sorrow.
Example: “The accident resulted in grievous injuries.”
It is derived from the word “grieve,” which means to feel deep sorrow or distress.

Correct Answer: C. Present Perfect Continuous Tense

The correct answer is:
C. Present Perfect Continuous Tense
Explanation:
The sentence “The sick child has been sleeping for three hours” uses the structure “has/have been + present participle” (in this case, sleeping), which is characteristic of the Present Perfect Continuous Tense.
This tense is used to describe an action that started in the past and is still continuing or has just recently finished, often with a focus on the duration of the action.

Correct Answer: D. Themselves

The correct answer is:
D. Themselves
Explanation:
The correct reflexive pronoun to use with “Scientists” (which is plural) is “themselves”.
Reflexive pronouns (myself, yourself, himself, herself, itself, ourselves, themselves) are used to refer back to the subject of the sentence, especially when the subject is performing the action on itself.
Correct Sentence:
“Scientists themselves are turning away from the cruder mechanical ideas.”

Correct Answer: D. Economical

The correct answer is:
D. Economical
Explanation:
The word “economical” refers to something that is efficient in terms of cost, such as “economical use of resources.”
The correct word to use in the context of discussing the country’s economic state is “economic”, which refers to matters related to the economy.
Why the Other Options Are Correct:
A. To: This is correct; the preposition “to” is used appropriately here.
B. Has organized: This is correct as the verb tense (present perfect) is used correctly.
C. Our: This is correct; “our” correctly refers to the possessive form of the subject.
Correct Sentence:
“Our University has organized a conference to discuss the economic conditions of the country.”

Correct Answer: C. Khaki and White

Let’s break down the information step by step:
We know the following facts:
There are three people: X, Y, Z.
They wore pants in three colors: Blue, Khaki, and Grey.
They wore shirts in three colors: White, Blue, and Pink.
No one wore pants and shirts of the same color.
Also, the conditions given are:
I. X did not wear a shirt of white color.
II. Y did not wear a shirt of blue color.
III. Z did not wear a shirt of pink color.
IV. Y did not wear pants of blue color.
V. Z wears pants of khaki color.
Step-by-Step Analysis:
From condition V:
Z wears Khaki pants.
Z cannot wear a pink shirt because of condition III (Z did not wear a pink shirt).
Therefore, Z must wear a blue shirt (the only remaining option).
From condition II:
Y did not wear a blue shirt, so Y must wear the pink shirt.
Since Y cannot wear blue pants (from condition IV), Y must wear the grey pants.
From condition I:
X did not wear a white shirt, and Y is already wearing the pink shirt. Therefore, X must wear the white shirt.
Since Z is wearing Khaki pants and Y is wearing grey pants, X must wear the blue pants.
Conclusion:
X wears blue pants and white shirt.
Final Answer: C. Khaki and white