Mountaineers carry oxygen cylinders because the amount of air (and oxygen) available at high altitudes is much less than that at ground level. As altitude increases, air pressure and oxygen concentration decrease, making breathing difficult and leading to altitude sickness. Supplemental oxygen helps them breathe properly and maintain body function.

• No air above 5 km: Incorrect — air exists but is thinner.
• Lower temperature: True but not the reason for carrying oxygen.
• Higher air pressure: Incorrect — pressure decreases with height.

Explanation: Minamata disease was caused by severe mercury poisoning in the coastal city of Minamata, Japan. It resulted from the discharge of methyl mercury compounds into Minamata Bay by a chemical factory (Chisso Corporation) during the 1950s and 1960s. The toxic mercury accumulated in fish and shellfish, which were later consumed by local residents. Symptoms included numbness, muscle weakness, loss of vision, hearing and speech, paralysis, and in severe cases, death. This incident is one of the world’s worst cases of industrial pollution.

Explanation: The term "Ozone hole" does not mean an actual hole but refers to a significant decrease in the thickness of the ozone layer in the Earth's stratosphere. This thinning occurs mainly over the Antarctic region during spring (September–November) due to chemical reactions involving chlorofluorocarbons (CFCs) and other ozone-depleting substances. These chemicals release chlorine and bromine atoms, which destroy ozone (O₃) molecules. The thinning allows more harmful ultraviolet (UV) radiation to reach the Earth's surface, causing health and environmental hazards.

Explanation: A strong-smelling compound called thioethanolamine (or ethyl mercaptan) is added to LPG (liquefied petroleum gas) to help detect gas leaks. LPG itself is odourless, so this compound gives it a distinct unpleasant smell, making leakage easily noticeable for safety.

Explanation: A transformer is an electrical device used to increase (step-up) or decrease (step-down) the voltage of alternating current (A.C.). It works on the principle of electromagnetic induction and functions only with A.C., not with D.C. A transformer consists of two coils—primary and secondary—wound around a soft iron core. The voltage ratio between these coils depends on the number of turns in each winding. Transformers are used in power transmission, distribution, and electronic devices to regulate voltage levels efficiently.

Explanation: Mumps is a contagious viral disease caused by the mumps virus, a member of the Paramyxoviridae family (genus Rubulavirus). It primarily affects the salivary glands, especially the parotid glands, leading to painful swelling near the cheeks and jawline.

Mode of Transmission: The infection spreads through respiratory droplets or direct contact with saliva from an infected person.

Symptoms:

• Swelling and pain in the parotid glands (below the ears)
• Fever and headache
• Muscle pain and fatigue
• Difficulty in chewing or swallowing

Prevention: Mumps can be effectively prevented by the MMR vaccine (Measles, Mumps, and Rubella vaccine).

Explanation: In humans, the spinal cord gives rise to 31 pairs of spinal nerves. Each spinal nerve is a mixed nerve containing both sensory and motor fibers. They are divided into groups based on the region of the vertebral column from which they originate:

• 8 pairs — Cervical nerves
• 12 pairs — Thoracic nerves
• 5 pairs — Lumbar nerves
• 5 pairs — Sacral nerves
• 1 pair — Coccygeal nerve

These spinal nerves connect the central nervous system (CNS) to different parts of the body, transmitting sensory information to the brain and motor commands to muscles.

Explanation: The blue whale (Balaenoptera musculus) holds the record as the largest mammal and the largest living organism on Earth. Adult blue whales can reach lengths of up to 30 meters (98 feet) and weigh over 180 tons. Despite their size, they feed mainly on small shrimp-like creatures called krill, filtering them through their baleen plates. Whales are warm-blooded, breathe air through blowholes, and give birth to live young — all key mammalian traits.

Comparison:

• Blue whale (largest mammal): up to 30 m long, ~180 tons
• African elephant (largest land mammal): up to 4 m tall, ~6 tons
• Rhinoceros: up to 2 m tall, ~2 tons

Aluminium (Al) is the most abundant metal in the Earth's crust, making up about 8.2% by weight. It occurs mainly in the form of bauxite ore (Al₂O₃·2H₂O). Despite being highly abundant, aluminium is never found in its pure form naturally due to its strong reactivity with oxygen. It is widely used in industries for making utensils, aircraft parts, electrical wires, and packaging materials.

Other options (for context)

• Zinc: Found in smaller quantities; used in galvanization and alloys.
• Copper: Less abundant; mainly used in electrical wiring.
• Iron: Very abundant but ranks below aluminium in crustal abundance.