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: Acid rain is caused by the presence of sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere. These gases are mainly released from the burning of coal, petroleum, and other fossil fuels in industries and vehicles. When they combine with water vapor and oxygen in the air, they form sulphuric acid (H₂SO₄) and nitric acid (HNO₃). These acids mix with rainwater and fall as acid rain, which damages soil, crops, aquatic life, and even monuments like the Taj Mahal.

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: Sound waves travel fastest in solids, slower in liquids, and slowest in gases. This is because the speed of sound depends on the elasticity and density of the medium — it travels faster when particles are tightly packed and can transmit vibrations more efficiently. Among the options, iron (a solid) allows sound to travel much faster (around 5130 m/s) than in water (1500 m/s), ice (3200 m/s), or air (331 m/s at 0°C).

Explanation: Tuberculosis (TB) is not a viral disease; it is caused by a bacterium called Mycobacterium tuberculosis. In contrast, Polio, Swine flu, and Hepatitis are viral diseases caused by different types of viruses.

Explanation: Opium is obtained from the latex present in the unripe capsule of the poppy plant (Papaver somniferum). The latex is collected by making incisions on the capsule, and after drying, it forms raw opium, which contains alkaloids like morphine and codeine.

Explanation: The King Cobra (Ophiophagus hannah) is the world’s longest venomous snake and the only snake species that builds a nest to lay its eggs. The female collects leaves, twigs, and debris to construct a mound-like nest, usually near dense vegetation or fallen logs. She lays about 20–40 eggs in the nest and guards them aggressively until they hatch, showing remarkable parental care — a rare behavior among reptiles.

Once the eggs are about to hatch, the female leaves the nest to avoid eating her own offspring, as King Cobras are carnivorous and feed mainly on other snakes.

Explanation: Human blood is maintained at a slightly alkaline pH of 7.4 (range 7.35–7.45). This balance is vital for the proper functioning of enzymes and biochemical reactions in the body. The buffer systems in blood — primarily the bicarbonate buffer system (H₂CO₃ / HCO₃⁻) — help maintain this stable pH. A small deviation from this range can lead to severe physiological disturbances.

Imbalances:

• Acidosis: pH below 7.35 — causes drowsiness, confusion, and respiratory distress.
• Alkalosis: pH above 7.45 — causes muscle twitching, irritability, and convulsions.

Explanation: Nuclear fission is the process in which the nucleus of a heavy atom, such as Uranium-235 or Plutonium-239, splits into two or more lighter nuclei when bombarded by a slow-moving neutron. This reaction releases a large amount of energy, along with additional neutrons that can trigger further fission reactions—leading to a chain reaction. This principle is used in nuclear reactors for power generation and in atomic bombs for explosive energy release.