Explanation: Cobalt-60 (Co-60) is a radioactive isotope of cobalt that emits high-energy gamma rays during its decay process. It decays into Nickel-60 (Ni-60) by beta decay, releasing two strong gamma photons of energies 1.17 MeV and 1.33 MeV. Due to these intense gamma emissions, Co-60 is widely used in radiation therapy (teletherapy) for cancer treatment, as well as in industrial radiography and sterilization of medical equipment. Gamma rays have high penetration power, allowing them to destroy cancerous cells deep inside tissues.

The electron was discovered by J. J. Thomson in 1897 during his experiments with cathode rays. He demonstrated that cathode rays are composed of tiny negatively charged particles, which he named electrons. This discovery revolutionized atomic theory and led to the development of the plum pudding model of the atom, where electrons are embedded in a positively charged sphere.

Other options (for context)

• Enrico Fermi: Known for his work on nuclear physics and the development of the first nuclear reactor.
• Robert Noyce: Co-inventor of the integrated circuit (microchip).
• James Dyson: Inventor of the modern vacuum cleaner, not a physicist.

Explanation: Anaemia is a condition caused by a deficiency of iron in the body, leading to reduced formation of haemoglobin in red blood cells. As a result, the blood’s capacity to carry oxygen decreases, causing fatigue, weakness, dizziness, and pale skin. Iron is essential for haemoglobin synthesis, and deficiency can result from poor diet, blood loss, or malabsorption. Foods rich in iron include green leafy vegetables, liver, red meat, legumes, and jaggery.

Explanation: The flow of electrons through a metallic wire constitutes an electric current. In metals, free electrons move from the negative terminal to the positive terminal of a power source, while the conventional direction of current is taken as opposite — from positive to negative.

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: 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: Ascorbic acid is not a member of the vitamin B complex; it is actually vitamin C. The vitamin B complex includes vitamins like thiamine (B₁), riboflavin (B₂), niacin (B₃), folic acid (B₉), and others that play important roles in metabolism and energy production.