Explanation: Organic farming is an agricultural method that emphasizes the use of natural inputs and eco-friendly techniques. It avoids chemical fertilizers, pesticides, and genetically modified organisms (GMOs). Instead, it uses organic manures (compost, green manure, and farmyard manure), crop rotation, and biological pest control to maintain soil health and productivity. Chemical fertilizers are excluded because they degrade soil quality and harm beneficial soil organisms over time.

Explanation: The habitat of an organism is its natural living place where it finds food, water, shelter, and mates for reproduction. Examples include a pond for a frog, soil for an earthworm, and forest for a tiger. Each species has a specific habitat suited to its survival needs. The niche, on the other hand, describes the organism’s role or function in that habitat, such as how it obtains food or interacts with others.

Explanation: Minamata disease was caused by severe mercury poisoning in the coastal city of Minamata, Japan. It resulted from the discharge of methyl mercury compounds into Minamata Bay by a chemical factory (Chisso Corporation) during the 1950s and 1960s. The toxic mercury accumulated in fish and shellfish, which were later consumed by local residents. Symptoms included numbness, muscle weakness, loss of vision, hearing and speech, paralysis, and in severe cases, death. This incident is one of the world’s worst cases of industrial pollution.

Explanation: The onion is a modified underground stem called a bulb. It consists of a short, disc-like stem (the basal plate) surrounded by concentric fleshy leaf bases that store food. The roots emerge from the underside of the basal plate, and new shoots grow from the center. Thus, the onion bulb serves as a storage organ for nutrients and helps in vegetative propagation.

Explanation: The rusting of iron is an example of oxidation. When iron reacts with oxygen and moisture from the air, it forms hydrated ferric oxide (Fe₂O₃·xH₂O), commonly known as rust. This process involves the loss of electrons by iron, which is a characteristic feature of oxidation.

Insulin was discovered by Frederick Banting and Charles Best in 1921 at the University of Toronto. Banting and his team successfully isolated insulin from the pancreas, which became a breakthrough in the treatment of diabetes mellitus. For this discovery, Frederick Banting and J.J.R. Macleod were awarded the Nobel Prize in Physiology or Medicine in 1923.

Other options (for context)

• Jonas E. Salk: Discovered the first successful polio vaccine.
• Alexander Fleming: Discovered penicillin, the first antibiotic.
• Roentgen: Discovered X-rays in 1895.

Explanation: Humans first develop a set of 20 milk teeth (also called deciduous or primary teeth) — 10 in the upper jaw and 10 in the lower jaw. These teeth start erupting around 6 months of age and are eventually replaced by 32 permanent teeth (including 4 wisdom teeth). Milk teeth help in early chewing, speaking, and maintaining space for permanent teeth.

Explanation: The branch of science that deals with the study of the production, behavior, and effects of materials at very low temperatures is called Cryogenics. The word comes from the Greek words “kryos” meaning cold and “gen” meaning to produce. Cryogenics involves cooling substances to temperatures below −150°C (123 K). It has applications in liquefying gases (like oxygen and nitrogen), cryopreservation of biological samples, superconductivity research, and rocket fuel storage (e.g., liquid hydrogen and oxygen).

Explanation: According to the Bureau of Indian Standards (BIS) – IS 10500:2012, the acceptable limit of total hardness in drinking water, expressed as CaCO₃, is 200 mg/l. The permissible limit in the absence of an alternate source is up to 600 mg/l. Excess hardness can cause scaling and affect the taste of water.