Explanation: A mirage is an optical illusion caused by both refraction and total internal reflection of light. It occurs when light rays bend due to temperature variations in air layers near the ground, creating the illusion of water or a reflected image on hot surfaces like roads or deserts.

Explanation: Although most non-metals do not conduct electricity, graphite is an exception. In graphite, each carbon atom is bonded to three others, leaving one free electron that moves freely between layers, allowing it to conduct electricity efficiently.

Running water is the source of hydel power (also called hydroelectric power). The energy of flowing or falling water is converted into electrical energy using turbines and generators in dams. It is a renewable, clean, and sustainable source of energy widely used in India and worldwide.

• Thermal power: Generated by burning coal or other fuels.
• Nuclear power: Produced from nuclear fission reactions.
• None of the above: Incorrect — running water directly produces hydel power.

Explanation: The Montreal Protocol, signed in 1987, is an international agreement aimed at protecting the ozone layer by phasing out the production and use of ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs) and halons. It is one of the most successful environmental treaties in history.

Explanation: The heart is enclosed in a double-layered protective membrane called the pericardium. The outer fibrous layer protects the heart and anchors it within the chest cavity, while the inner serous layer secretes pericardial fluid that reduces friction during heartbeats. This fluid-filled sac ensures smooth and cushioned movement of the heart as it contracts and relaxes continuously.

Explanation: Respiration is a biochemical process in which food molecules (mainly glucose) are oxidized to release energy in the form of ATP (adenosine triphosphate). This energy is then used for various life processes such as movement, growth, repair, and maintenance. Respiration occurs in all living cells and takes place mainly inside the mitochondria.

Chemical Equation:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

In contrast, photosynthesis stores energy in glucose molecules, while respiration releases that stored energy for cellular use.

Explanation: When a bus starts suddenly, the passengers tend to lean backward due to the inertia of rest. Inertia is the tendency of a body to resist any change in its state of motion or rest. The lower part of the passenger’s body moves forward with the bus as it starts, but the upper part of the body tends to remain at rest momentarily. This makes the passenger appear to fall backward relative to the bus. It is a clear example of Newton’s First Law of Motion.