Explanation: When a man inside a moving train tosses a coin and it falls behind him, it means the train is moving forward with acceleration. The coin, after being tossed, continues to move with the train’s initial velocity, but since the train speeds up, the coin appears to fall backward relative to the man.

Insecticides primarily act upon the nervous system of insects. They interfere with the transmission of nerve impulses, leading to paralysis and ultimately death. Common insecticides like organophosphates and carbamates inhibit the enzyme acetylcholinesterase, causing continuous nerve stimulation. Some others, like pyrethroids, disrupt sodium channel functioning in nerve cells.

Other options (for context)

• Muscular system: Indirectly affected due to nerve failure, but not the primary target.
• Digestive system: Rarely affected — insecticides mainly disrupt neural signaling, not digestion.

Explanation: The biosphere is the global sum of all ecosystems — it encompasses every region of Earth where living organisms are found. It includes portions of the lithosphere (land), hydrosphere (water), and atmosphere (air) that support life. The biosphere extends from deep ocean trenches to the lower layers of the atmosphere where microorganisms can survive.

Explanation: In India, the largest share of electricity generation comes from thermal power. Thermal power plants generate electricity by using heat energy, primarily produced by burning coal, natural gas, or oil. Among these, coal-based thermal power contributes the majority. Although renewable sources like solar and hydro power are growing rapidly, thermal energy still accounts for over 70% of India’s total electricity production. This dominance is due to the abundant availability of coal and the extensive infrastructure built around it.

Nickel exposure commonly causes a skin disease called Dermatitis, specifically Allergic Contact Dermatitis. This condition occurs when the skin comes into direct contact with nickel-containing objects such as jewelry, coins, or belt buckles. It leads to redness, itching, and rashes, especially in sensitive individuals. Nickel allergy is one of the most common metal allergies worldwide.

Other options (for context)

• Itai Itai: Caused by cadmium poisoning, not nickel.
• Learning Disability: Not directly linked to nickel exposure.
• Asthma: May be aggravated by pollutants, but not typically caused by nickel.

When an ant bites, it releases formic acid (HCOOH) into the skin. This acid causes a sharp burning sensation, redness, and irritation at the site of the bite. The name “formic” comes from the Latin word “formica”, meaning ant, as the acid was first extracted from ants. The pain can be neutralized by applying a mild base like baking soda (sodium bicarbonate).

Other options (for context)

• Hydrochloric Acid: Found in the human stomach, aids digestion.
• Acetic Acid: Main component of vinegar, not involved in ant bites.
• Phosphoric Acid: Used in fertilizers and soft drinks, not produced by ants.

Carbon dioxide (CO₂) is commonly used as a fire extinguisher gas. It works by displacing oxygen around the fire and forming a blanket of gas that cuts off the oxygen supply, thereby stopping the combustion process. Additionally, CO₂ is non-flammable and leaves no residue, making it ideal for use on electrical and electronic fires where water cannot be used safely.

Other options (for context)

• Nitrogen dioxide (NO₂): A toxic gas, not suitable for firefighting.
• Carbon monoxide (CO): A poisonous gas produced by incomplete combustion, not used in extinguishers.
• Nitrous oxide (N₂O): Commonly known as laughing gas, used as an anesthetic, not a fire suppressant.

The Ramsar Convention is an international treaty for the conservation and sustainable use of wetlands. Signed in 1971 at Ramsar, Iran, it aims to preserve wetlands as habitats for biodiversity, especially for migratory birds. It promotes wise use of wetland ecosystems through local and national actions.

• Mountain: Conserved under other ecological programs.
• Grassland: Managed under terrestrial biodiversity initiatives.
• Forest: Covered under the UN Forest Forum, not Ramsar.