Explanation: Natural gas is not a renewable source of energy because it is a fossil fuel formed over millions of years from the remains of plants and animals. Once used, it cannot be replenished quickly. In contrast, geothermal energy, flowing water, and biomass are renewable energy sources that can be naturally regenerated.

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.

Explanation: The element hydrogen is common to all acids. Acids are substances that produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺) when dissolved in water. This property gives acids their characteristic sour taste, the ability to turn blue litmus paper red, and to react with bases to form salts and water. Examples include hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃)—all of which release hydrogen ions in aqueous solution.

Explanation: Ecology is a branch of biology that deals with the relationships of living organisms with one another and with their physical surroundings. It examines how organisms adapt to their environment, how energy flows through ecosystems, and how matter cycles within the biosphere. The term “Ecology” was first coined by Ernst Haeckel in 1866.

Explanation: Lysosomes are known as the ‘suicidal bags’ or ‘disposal units’ of the cell because they contain powerful digestive enzymes capable of breaking down worn-out cell parts, foreign substances, and even the entire cell when it becomes damaged or obsolete.

The Abacus is considered the first calculating device in human history. It was invented around 2500 BCE and used in ancient civilizations such as China, Egypt, and Mesopotamia. The Abacus consists of beads that slide on rods or wires, representing numbers, and is used to perform basic arithmetic operations like addition, subtraction, multiplication, and division. It laid the foundation for modern computing and calculating tools.

Other options (for context)

• Calculator: A modern electronic device for computation, developed much later.
• Turing machine: A theoretical computational model proposed by Alan Turing in 1936.
• Pascaline: A mechanical calculator invented by Blaise Pascal in 1642, long after the Abacus.

Sputnik I was the first artificial satellite to orbit the Earth. It was launched by the Soviet Union on October 4, 1957. The successful launch of Sputnik I marked the beginning of the space age and initiated the space race between the USA and the USSR.

• Explorer I: First U.S. satellite, launched in 1958.
• Vanguard I: A U.S. satellite launched later in 1958.
• Discoverer I: Part of an American reconnaissance satellite program (1959).

Explanation: Neutron was discovered by James Chadwick in 1932. He identified the neutron as a neutral subatomic particle present in the nucleus of an atom, having a mass nearly equal to that of a proton but no electrical charge.

The Yellow Revolution in India refers to the significant increase in the production of oilseeds. It was initiated to make India self-sufficient in edible oils such as mustard, sunflower, groundnut, and soybean oils. The revolution gained momentum under the Technology Mission on Oilseeds (TMO) launched in the 1980s. The key figure associated with the Yellow Revolution is Sam Pitroda.

Other options (for context)

• Cereals: Their production growth is linked with the Green Revolution.
• Milk: Related to the White Revolution led by Dr. Verghese Kurien.
• None of these: Incorrect — the Yellow Revolution specifically concerns oilseeds.

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.