Explanation: Alternating current (AC) is used for long-distance transmission because energy losses are minimal. The voltage of AC can be easily increased or decreased using transformers, allowing transmission at high voltage and low current, which reduces power loss due to resistance in the wires.

Explanation: Thiamine (Vitamin B₁) is a water-soluble vitamin essential for carbohydrate metabolism and proper functioning of the nervous system. Its deficiency causes beriberi, which manifests as muscle weakness, loss of appetite, fatigue, and nerve degeneration. There are two main types of beriberi: dry beriberi (affecting nerves) and wet beriberi (affecting the heart).

Rich Sources: Whole grains, legumes, nuts, meat, eggs, and yeast.

Explanation: The pale yellow color of normal human urine is due to the presence of a pigment called Urochrome. It is produced from the breakdown of hemoglobin in red blood cells. The intensity of the color depends on the concentration of the urine — darker yellow indicates concentrated urine, while very pale or colorless urine suggests dilution due to high water intake.

Explanation: A rainbow is formed due to the dispersion of sunlight into its constituent colors and total internal reflection inside water droplets in the atmosphere. The light entering a droplet is refracted, reflected internally, and then refracted again as it exits, producing the beautiful spectrum of colors.

Green leafy vegetables are a rich source of Folic Acid (Vitamin B₉). Folic acid is essential for the formation of red blood cells, DNA synthesis, and proper cell growth. It is particularly important for pregnant women, as it helps prevent neural tube defects in the developing fetus. Vegetables like spinach, kale, lettuce, and fenugreek leaves are excellent sources of folic acid.

Other options (for context)

• Citric acid: Found mainly in citrus fruits like oranges and lemons.
• Malic acid: Commonly present in apples and other fruits, not in leafy greens.
• None of these: Incorrect — folic acid is the correct nutrient associated with green leafy vegetables.

Explanation: Neutron was discovered by James Chadwick in 1932. He identified the neutron as a neutral subatomic particle present in the nucleus of an atom, having a mass nearly equal to that of a proton but no electrical charge.

Xylem is a type of vascular tissue in plants responsible for the transportation of water and dissolved minerals from the roots to the stems and leaves. The upward movement of water through xylem vessels occurs due to processes like transpiration pull, root pressure, and capillary action. Xylem also provides mechanical support to the plant.

Other options (for context)

• Food: Transported by phloem, not xylem.
• Nutrient: Minerals are carried along with water but the primary function of xylem is water transport.
• Both food and water: Incorrect — only phloem transports food; xylem transports water.

Nitrous oxide (N₂O) is an anaesthetic gas, commonly known as laughing gas. It is used in dentistry and minor surgeries to induce mild anesthesia and relaxation. It acts quickly and wears off rapidly, making it safe for short medical procedures.

• Nitrogen dioxide: A toxic air pollutant, not used as anesthesia.
• Nitric oxide: A signaling molecule in the body, not an anesthetic.
• Nitrogen: An inert gas, does not induce anesthesia.