Explanation: Asbestos is a group of silicate minerals once used in insulation and construction materials. Inhalation of asbestos fibers causes severe lung disorders such as asbestosis and emphysema, leading to breathing difficulty, chest pain, and even lung cancer (mesothelioma). The fibers lodge in lung tissue and trigger inflammation and fibrosis over time.

The purity of milk is tested using a Lactometer. It works on the principle of Archimedes’ principle and is used to measure the specific gravity (density) of milk. Pure milk has a specific gravity ranging between 1.026 and 1.032. If water or other substances are added, the density decreases, indicating adulteration. The lactometer thus helps determine whether the milk is pure or diluted.

Other options (for context)

• Electrometer: Measures electric potential or charge, not related to milk testing.
• Radiometer: Measures radiant energy or light intensity.
• Refractometer: Used to measure refractive index, commonly for sugar solutions, not milk purity.

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: Light from the Sun takes approximately 8 minutes and 20 seconds to reach the Earth. The average distance between the Earth and the Sun is about 149.6 million kilometers (1 Astronomical Unit). Since light travels at a speed of 3 × 10⁸ meters per second in a vacuum, it covers this distance in roughly eight minutes. This means that when we see sunlight, we are actually seeing it as it was about eight minutes earlier.

PINAKA is an indigenously developed Multi Barrel Rocket Launch (MBRL) system designed and produced by the Defence Research and Development Organisation (DRDO) of India. It is capable of firing a salvo of rockets to deliver explosive warheads over large areas with high accuracy. Pinaka is primarily used by the Indian Army for long-range artillery support and has a range of up to 75 km in its upgraded version (Pinaka Mk-II).

Other options (for context)

• Anti-submarine torpedo and research vehicle: Refers to underwater weapon systems, not related to Pinaka.
• Aircraft carrier: A large naval vessel capable of carrying aircraft; Pinaka is not a ship.
• Guided missile frigate submarine warship: Refers to naval warships, not a land-based rocket launcher.

Brown is not seen in a rainbow. A natural rainbow displays seven distinct colours — Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). These colours appear due to the dispersion of sunlight by water droplets in the atmosphere, but brown is not part of the visible spectrum formed by dispersion.

• Yellow, Green, Red: All are part of the seven colours of the rainbow.

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: Producer gas is a mixture of flammable gases such as carbon monoxide (CO) and hydrogen (H₂), along with nonflammable gases like nitrogen (N₂) and carbon dioxide (CO₂). It is produced by the partial combustion of carbon-containing fuels (like coal or coke) with air and steam, and is used as a fuel in industrial furnaces.