Explanation: Vitamin B₁₂, also known as Cobalamin, is the only vitamin that contains a metal ion — cobalt (Co) — at its core. It plays a crucial role in red blood cell formation, DNA synthesis, and proper nervous system function. Deficiency of Vitamin B₁₂ leads to pernicious anemia and neurological disorders. It is found mainly in animal-based foods such as meat, eggs, milk, and fish, and is synthesized by certain bacteria.

Explanation: The terms Dolby B and Dolby C refer to noise reduction circuits used in tape recorders and sound systems. These technologies reduce background hiss and unwanted noise during playback and recording, thereby improving the overall sound quality.

Explanation: A light year is a unit used to measure stellar or astronomical distances. It is defined as the distance that light travels in one year in a vacuum. Since light moves at a speed of about 3 × 10⁸ m/s, one light year equals approximately 9.46 × 10¹² km. It is commonly used to express distances between stars and galaxies because these distances are too large to be measured in kilometers or miles.

Explanation: A rainbow is formed in the part of the sky opposite to the Sun. It occurs when sunlight is refracted, internally reflected, and dispersed by raindrops, splitting the light into its seven constituent colors. The observer must have the Sun behind them and rain in front to see the rainbow clearly.

Explanation: The Olive Ridley turtle (Lepidochelys olivacea) is the smallest and most abundant species of sea turtle found primarily in warm and tropical waters, including the Indian Ocean. It is named for the olive color of its shell. These turtles are famous for their unique mass nesting phenomenon known as “arribada”, where thousands of females come ashore simultaneously to lay eggs. In India, large nesting sites are found along the coast of Odisha, especially at Gahirmatha Beach and the Rushikulya River mouth.

Explanation: A lens is generally made of flint glass, which contains lead oxide. Flint glass has a higher refractive index than ordinary glass, allowing it to bend light more effectively. This property makes it ideal for manufacturing optical instruments such as lenses and prisms.

Explanation: A solar eclipse occurs when the Moon comes between the Sun and the Earth and casts its shadow on the Earth. This happens during the new moon phase, when all three celestial bodies are almost in a straight line. Depending on the alignment, the eclipse can be total (Sun completely covered), partial (Sun partially covered), or annular (ring-shaped Sun visible). During this event, sunlight is blocked for a short time in specific areas of the Earth’s surface.

Explanation: Bronchitis is an inflammation of the bronchial tubes, which are the air passages of the respiratory tract that carry air to and from the lungs. The condition causes coughing, mucus production, chest discomfort, and difficulty in breathing. It can be caused by viral or bacterial infections, long-term exposure to smoke, dust, or air pollutants. Chronic bronchitis is a serious form often associated with smoking and is part of a group of lung diseases known as COPD (Chronic Obstructive Pulmonary Disease).

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.