General Science

Raindrops become spherical due to surface tension, which is the cohesive force between water molecules. Surface tension minimizes the surface area for a given volume, and a sphere has the smallest possible surface area. Friction, atmospheric pressure, and viscosity affect raindrop size and fall speed but not their fundamental shape.

Organisms survive at the bottom of frozen lakes because water at the bottom remains liquid due to water's unique density properties. Water is densest at 4°C, so the coldest water sinks and freezes at the surface, creating an insulating ice layer while warmer water (around 4°C) stays at the bottom, allowing aquatic life to survive.

ELISA (Enzyme Linked Immunosorbent Assay) is commonly used to detect HIV/AIDS antibodies in blood samples. While ELISA can be adapted to detect various infectious diseases including typhoid and tuberculosis, it is most widely known and used as the initial screening test for HIV infection.

A physical balance works on the principle of moments (torque equilibrium). When the balance is level, the clockwise moment equals the anticlockwise moment. The product of mass and distance from the fulcrum must be equal on both sides for equilibrium to be achieved, which is the fundamental principle behind weighing scales.

Heavy water (D2O - deuterium oxide) is used as a moderator in nuclear reactors. It slows down neutrons effectively to sustain the nuclear chain reaction while absorbing fewer neutrons than light water. Heavy water's neutron moderation properties make it essential for certain types of nuclear reactors, particularly those using natural uranium.

Normal human body temperature is approximately 36.8°C (98.6°F) when measured orally. Option B (98.60°C) is incorrect as it represents boiling temperature, not body temperature. The correct answer is A which matches the standard normal body temperature.

Planets are non-luminous celestial bodies that do not twinkle (Option A). They reflect sunlight and appear steady because they are much closer to Earth compared to stars. Stars twinkle due to atmospheric turbulence, but planets do not.

Green leafy vegetables (Option C) are indeed rich sources of iron, which is essential for hemoglobin formation and preventing anemia. Options like mutton, curd, and potato are not as iron-dense as leafy greens such as spinach, kale, and fenugreek.

The first TB vaccine (BCG - Bacille Calmette-Guérin) was developed by Leon Calmette and Camille Guérin (Option C). This is historically accurate. Joseph Lister is known for antiseptic surgery, W.J. Kolff for dialysis machines, and the Curies for radioactivity research.

Iodine deficiency causes goitre (Option B), which is the enlargement of the thyroid gland. The thyroid gland requires iodine to produce hormones, and deficiency leads to compensatory enlargement. Gigantism is caused by growth hormone excess, cretinism by severe congenital hypothyroidism, and diabetes by insulin deficiency.

The microscope was invented by Zacharias Jansen (Option A). Jansen, a Dutch spectacle maker, is credited with inventing the first compound microscope around 1590. The other names listed are not associated with microscope invention.

Gasoline is popularly known as petrol (Option D). In Commonwealth countries like India and UK, gasoline is called petrol. 'Petrol gas' is redundant, 'naphtha' is a different petroleum product, and 'asphalt' is used for roads.

Vitamins (Option A) are the most heat-sensitive nutrients and are lost in maximum quantities during cooking. Water-soluble vitamins like Vitamin C and B-complex are particularly vulnerable to heat and leaching into cooking water. Carbohydrates, proteins, and fats are relatively more stable.

The main active constituent of tea and coffee is caffeine (Option B), which is a central nervous system stimulant. Reserpine is a blood pressure medication, 'asphin' appears to be a misspelling or nonexistent term, and morphine is an opioid painkiller.

Petrol is obtained from crude oil by the process of fractional distillation (Option C). This process separates petroleum products based on their boiling points. Crystallization forms solid crystals, decantation separates immiscible liquids, and sublimation converts solid directly to gas.

The liver is the primary organ responsible for metabolizing alcohol. Excessive alcohol consumption causes fatty liver, alcoholic hepatitis, and eventually cirrhosis - permanent scarring of liver tissue. The liver breaks down alcohol, but this process produces toxic byproducts that damage liver cells over time.

In energy classification, conventional sources refer to those used traditionally for a long time, like coal, petroleum, natural gas, and hydroelectricity. Non-conventional or renewable sources include solar, wind, geothermal, tidal, and biogas. Among the options, only hydroelectricity is classified as conventional, while geothermal, biogas, and solar are non-conventional sources.

Amniocentesis (note the correct spelling) is a prenatal test where a small amount of amniotic fluid is extracted from the amniotic sac. While it can determine fetal sex, its primary purpose is detecting chromosomal abnormalities and genetic disorders like Down syndrome. Sex determination for selective abortion is illegal in India.

Hypokalemia is the medical term for low potassium levels in the blood. Potassium is an essential electrolyte that helps regulate nerve signals, muscle contractions, and heart rhythm. The prefix 'hypo-' means deficient or low, and '-kal' refers to potassium (chemical symbol K).

Saliva contains the enzyme salivary amylase (also called ptyalin), which begins the breakdown of starch into simpler sugars like maltose. This is the first step of carbohydrate digestion. Saliva does not contain enzymes that digest proteins (requires pepsin/trypsin) or fats (requires lipase). Fiber is indigestible by human enzymes.

National Science Day in India is celebrated on February 28th each year to commemorate the discovery of the Raman Effect by Sir C.V. Raman in 1928, for which he was awarded the Nobel Prize in Physics in 1930. The day honors scientific achievements and promotes science awareness in India.