Sericulture is the rearing and cultivation of silkworms for the production of silk. The process involves raising silkworms on mulberry leaves, harvesting their cocoons, and then extracting silk fibers from these cocoons. The most commonly used silkworm species is Bombyx mori. Sericulture is an important cottage industry in countries like India, China, and Japan.

Other options (for context)

• Fishes: Their rearing is called Pisciculture.
• Honey bees: Their rearing is called Apiculture.
• Earth worms: Their cultivation for composting is called Vermiculture.

Explanation: Seismology is the branch of geophysics that deals with the study of earthquakes and the propagation of seismic waves through the Earth. Scientists who study earthquakes are called seismologists. Seismology helps in understanding the origin, intensity, and effects of earthquakes, as well as the internal structure of the Earth. The intensity of an earthquake is measured using instruments like the seismograph and scales such as the Richter scale or Moment Magnitude scale.

Explanation: In fused (molten) sodium chloride, electric current passes due to the presence of free ions. When solid NaCl is melted, it dissociates into Na⁺ and Cl⁻ ions, which can move freely and conduct electricity. In the solid state, these ions are fixed in the crystal lattice, so it does not conduct electricity.

Explanation: Lysergic acid diethylamide (LSD) was discovered by Dr. Albert Hofmann, a Swiss chemist, in 1938 at the Sandoz Laboratories in Switzerland. LSD is a powerful hallucinogenic compound derived from lysergic acid, which occurs in the fungus Claviceps purpurea (ergot) that grows on rye. Hofmann accidentally discovered its psychological effects in 1943 when he absorbed a small amount through his skin, leading to vivid visual hallucinations. LSD acts on serotonin receptors in the brain and profoundly alters perception and mood.

Explanation: In an incompatible blood transfusion, the antibodies in the recipient’s plasma bind to the antigens on the donor’s RBCs. This causes the red blood cells to agglutinate (clump together) and eventually undergo hemolysis (bursting). The released hemoglobin can block kidney tubules and cause kidney failure, which can be fatal if untreated. This is why blood group compatibility testing (cross-matching) is essential before transfusions.

Example:

If a person with blood group B (having anti-A antibodies) receives blood from a person with group A (which has A antigens), the recipient’s anti-A antibodies will attack the donor’s RBCs, leading to agglutination.

Explanation: The colour of the sky without an atmosphere would appear black. On Earth, the sky looks blue because molecules in the atmosphere scatter sunlight — a phenomenon called Rayleigh scattering. Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (red). However, if there were no atmosphere to scatter sunlight, no light would be diffused in all directions, and the sky would appear completely dark or black, just as it does from the surface of the Moon or in outer space.

Explanation: A barometer is an instrument used primarily for measuring atmospheric pressure. It helps in weather forecasting and determining altitudes (since atmospheric pressure decreases with height). A mercury barometer consists of a glass tube filled with mercury inverted in a mercury reservoir. When air pressure changes, the height of the mercury column changes accordingly. However, a barometer cannot measure the density of a liquid — that function is performed by a hydrometer.

The gravitational force of the Earth is maximum at the poles and minimum at the equator. This happens because the Earth is not a perfect sphere; it is slightly flattened at the poles and bulged at the equator due to its rotation. The distance from the center of the Earth to the poles is slightly less than that to the equator, resulting in a stronger gravitational pull at the poles.

Other options (for context)

• At equator: Gravity is slightly weaker because of the Earth's bulge and centrifugal force due to rotation.
• At tropic of cancer: Gravity here is intermediate, not maximum.
• At tropic of Capricorn: Same as the Tropic of Cancer — gravity is moderate, not maximum.

Explanation: Kala-azar, also known as visceral leishmaniasis, is caused by the protozoan parasite Leishmania donovani. It is transmitted through the bite of the female Phlebotomus sandfly. The disease primarily affects the liver, spleen, and bone marrow, leading to symptoms such as fever, anemia, weight loss, and darkening of the skin. The term “Kala-azar” literally means “black fever.”