Explanation: Brass, an alloy of copper and zinc, gets discoloured when exposed to air containing hydrogen sulphide (H₂S). The H₂S reacts with the metal surface to form a dark layer of metal sulphides (mainly copper sulphide), causing tarnishing and loss of shine.

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.

The physical quantity measured in kg·m/s² is Force. The SI unit of force is the Newton (N), which is defined as the force required to accelerate a mass of 1 kilogram by 1 meter per second squared. Mathematically, Force = Mass × Acceleration.

• Work: Measured in joules (N·m).
• Power: Measured in watts (J/s).
• Motion: Describes movement, not a measurable quantity in these units.

Explanation: The statement “Exercise does not help in managing psychological discomfort” is incorrect. Regular physical exercise helps reduce stress, anxiety, and depression by releasing endorphins — the body’s natural mood enhancers. It also improves overall mental health, cardio-respiratory fitness, reduces the risk of diabetes, and strengthens bones.

The Kyoto Protocol is an international agreement related to the environment, specifically aimed at reducing greenhouse gas emissions that contribute to global warming and climate change. It was adopted in Kyoto, Japan, in 1997 and came into force in 2005. The protocol set binding targets for developed countries to limit or reduce their carbon dioxide (CO₂) and other greenhouse gas emissions.

Other options (for context)

• Nuclear Power: Not the focus of the Kyoto Protocol; this relates to energy generation and atomic energy regulation.
• Trade: Covered under agreements like GATT and WTO, not the Kyoto Protocol.
• None of these: Incorrect — the Kyoto Protocol deals specifically with environmental protection.

Sericulture is the rearing and cultivation of silkworms for the production of silk. The process involves raising silkworms on mulberry leaves, harvesting their cocoons, and then extracting silk fibers from these cocoons. The most commonly used silkworm species is Bombyx mori. Sericulture is an important cottage industry in countries like India, China, and Japan.

Other options (for context)

• Fishes: Their rearing is called Pisciculture.
• Honey bees: Their rearing is called Apiculture.
• Earth worms: Their cultivation for composting is called Vermiculture.

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).

Explanation: The Cerebrum forms about 80% of the total brain mass. It is divided into two hemispheres and is responsible for higher brain functions such as thought, action, reasoning, and emotion. The Cerebellum lies below it and controls coordination and balance, while the Medulla oblongata manages vital involuntary functions.