The pale yellow colour of urine is due to the presence of the pigment Urochrome. Urochrome is a waste product formed from the breakdown of hemoglobin in red blood cells. It is produced when hemoglobin is metabolized into urobilin and then excreted through urine. The intensity of the yellow color can vary depending on hydration levels — darker urine indicates dehydration, while pale urine indicates proper hydration.

Other options (for context)

• Urophyll: No such pigment exists in human physiology.
• Chlorophyll: Green pigment found in plants, not in urine.
• Chloroplast: Cell organelle in plants where photosynthesis occurs, not a pigment.

Explanation: Mercury is the nearest planet to the Sun. It is the smallest planet in the solar system and completes one revolution around the Sun in just about 88 Earth days. Due to its proximity, Mercury experiences extreme temperature variations between day and night.

Insulin was discovered by Frederick Banting and Charles Best in 1921 at the University of Toronto. Banting and his team successfully isolated insulin from the pancreas, which became a breakthrough in the treatment of diabetes mellitus. For this discovery, Frederick Banting and J.J.R. Macleod were awarded the Nobel Prize in Physiology or Medicine in 1923.

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• Jonas E. Salk: Discovered the first successful polio vaccine.
• Alexander Fleming: Discovered penicillin, the first antibiotic.
• Roentgen: Discovered X-rays in 1895.

Explanation: Aerosols (such as those used in spray cans, refrigerants, and air conditioners) often contain chlorofluorocarbons (CFCs) and other halogen compounds. These chemicals rise to the stratosphere, where ultraviolet (UV) radiation breaks them down, releasing chlorine atoms. Each chlorine atom can destroy thousands of ozone (O₃) molecules, leading to ozone layer depletion. The thinning of the ozone layer allows more harmful UV rays to reach Earth, increasing the risk of skin cancer, eye damage, and affecting ecosystems.

Explanation: Penicillin was discovered accidentally by Alexander Fleming in 1928 when he observed that a fungal mold, Penicillium notatum, inhibited the growth of Staphylococcus bacteria in his culture plates. Penicillin became the first antibiotic used to treat bacterial infections and saved millions of lives during World War II. Later, scientists like Howard Florey and Ernst Boris Chain developed methods for its large-scale production.

Explanation: Fathom is a unit used to measure depth, particularly the depth of water in oceans and seas. One fathom is equal to 6 feet or approximately 1.83 meters. It is commonly used in navigation and marine studies.

Velocity is a vector quantity because it has both magnitude and direction. It represents the rate of change of displacement of an object. Unlike speed, which only tells how fast an object is moving, velocity also indicates the direction of motion.

Other options (for context)

• Mass: A scalar quantity — it has magnitude only, no direction.
• Volume: Scalar — represents space occupied by matter, without direction.
• Speed: Scalar — measures how fast an object moves but not in which direction.

Explanation: In GM food, the term GM stands for Genetically Modified. These are foods produced from organisms (plants or animals) whose genetic material (DNA) has been altered using modern biotechnology or genetic engineering techniques. This modification is done to introduce desirable traits such as pest resistance, drought tolerance, higher yield, or improved nutritional value. A common example is Bt cotton, which contains a gene from the bacterium Bacillus thuringiensis that provides resistance to insect pests.

Explanation: Cobalt-60 (Co-60) is a radioactive isotope of cobalt that emits high-energy gamma rays during its decay process. It decays into Nickel-60 (Ni-60) by beta decay, releasing two strong gamma photons of energies 1.17 MeV and 1.33 MeV. Due to these intense gamma emissions, Co-60 is widely used in radiation therapy (teletherapy) for cancer treatment, as well as in industrial radiography and sterilization of medical equipment. Gamma rays have high penetration power, allowing them to destroy cancerous cells deep inside tissues.

Explanation: Saliva, secreted by the salivary glands, begins the process of carbohydrate digestion in the mouth. It contains the enzyme salivary amylase (also known as ptyalin), which catalyzes the breakdown of starch (polysaccharide) into maltose (disaccharide). This is the first step in digestion, and it occurs while food is chewed and mixed with saliva before being swallowed.

Chemical Reaction:

Starch → (Salivary amylase) → Maltose

Thus, saliva plays an essential role in the digestion of carbohydrates, making the food slightly sweet when chewed for a longer time.