Explanation: The hard structure of bones and teeth is primarily made of calcium phosphate in the crystalline form of tricalcium phosphate (Ca₃(PO₄)₂). It provides rigidity and strength. In tooth enamel, a small portion is converted into fluorapatite, which makes teeth resistant to bacterial decay.

Explanation: A microscope uses a system of convex lenses to magnify very small objects. Convex lenses, also known as converging lenses, bend light rays inward to a focal point, creating an enlarged and clear image of the specimen. A compound microscope typically contains two sets of convex lenses — the objective lens (near the specimen) and the eyepiece lens (near the observer’s eye). The objective lens forms a real, inverted, and magnified image, which is then further magnified by the eyepiece to produce a large virtual image.

Explanation: Hydrogen (H₂) is a clean fuel that does not cause atmospheric pollution when burned. It combines with oxygen to produce water vapor (H₂O) as the only by-product, without emitting harmful gases like carbon monoxide (CO), carbon dioxide (CO₂), or sulphur dioxide (SO₂). Because of this, hydrogen is considered an eco-friendly and renewable energy source and is being promoted as the fuel of the future in hydrogen-powered vehicles and fuel cells.

Explanation: Ascorbic acid is not a member of the vitamin B complex; it is actually vitamin C. The vitamin B complex includes vitamins like thiamine (B₁), riboflavin (B₂), niacin (B₃), folic acid (B₉), and others that play important roles in metabolism and energy production.

Explanation: In household electrical wiring, all the given statements are correct: the red insulated wire is the live (phase) wire, the black insulated wire is the neutral wire, and the green insulated wire is used for earthing to ensure safety by preventing electric shocks.

Chandrayaan-2, launched by the Indian Space Research Organisation (ISRO) on 22 July 2019, was designed to explore the South Pole region of the Moon. This area is of great scientific interest because it is permanently shadowed and may contain water ice and other valuable minerals. The mission included an orbiter, a lander (Vikram), and a rover (Pragyan), making it India’s first attempt at a soft landing on the lunar surface near the south pole.

Other options (for context)

• Moon North Pole: Not the target area of Chandrayaan-2.
• Moon North-West part: Incorrect — Chandrayaan-2 focused specifically on the South Pole.
• Unexplored part of the Moon: Partly true, but specifically, the unexplored South Pole region was chosen.

Explanation: The tusks of elephants are actually modified second upper incisors. They are made primarily of dentine, commonly known as ivory, and covered by a thin layer of enamel at the tip (which wears off with time). Tusks grow continuously throughout the elephant’s life and are used for digging, lifting objects, stripping bark, defense, and dominance displays.

Note: Both male and female African elephants have tusks, whereas in Asian elephants, tusks are generally present only in males.

Composition: Tusks are composed of dentine (ivory) with fine concentric growth lines, and they grow from sockets in the skull.