Explanation: Nitrogen (N₂) constitutes the major portion of the Earth's atmosphere by volume — about 78%. It is a colorless, odorless, and inert gas that plays a vital role in maintaining atmospheric stability and supporting life through the nitrogen cycle. Oxygen makes up about 21% of the atmosphere and is essential for respiration and combustion. Other gases like argon (~0.93%) and carbon dioxide (~0.04%) are present in much smaller amounts.

Explanation: Asbestos is a group of silicate minerals once used in insulation and construction materials. Inhalation of asbestos fibers causes severe lung disorders such as asbestosis and emphysema, leading to breathing difficulty, chest pain, and even lung cancer (mesothelioma). The fibers lodge in lung tissue and trigger inflammation and fibrosis over time.

Explanation: A carnivore is an animal that primarily eats the flesh of other animals. The tiger (Panthera tigris) is a true carnivore and an apex predator in its ecosystem. It has sharp canines and retractable claws adapted for hunting and tearing flesh. Tigers play a vital role in maintaining the ecological balance by controlling herbivore populations in forests.

Green leafy vegetables are a rich source of Folic Acid (Vitamin B₉). Folic acid is essential for the formation of red blood cells, DNA synthesis, and proper cell growth. It is particularly important for pregnant women, as it helps prevent neural tube defects in the developing fetus. Vegetables like spinach, kale, lettuce, and fenugreek leaves are excellent sources of folic acid.

Other options (for context)

• Citric acid: Found mainly in citrus fruits like oranges and lemons.
• Malic acid: Commonly present in apples and other fruits, not in leafy greens.
• None of these: Incorrect — folic acid is the correct nutrient associated with green leafy vegetables.

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: 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: Antibodies (also called immunoglobulins) are specialized proteins produced by B-lymphocytes (a type of white blood cell) in response to the presence of foreign substances known as antigens (such as bacteria, viruses, or toxins). These antibodies recognize and bind specifically to the antigens to neutralize or destroy them, helping the body fight infections and build immunity. Antibodies are a vital part of the immune system and form the basis for vaccines and disease resistance.

Explanation: Sound travels fastest in steel because it is a solid material where the particles are packed very closely together. Sound waves need a medium to travel, and their speed depends on how quickly vibrations can pass from one particle to another. In solids, particles are tightly bound, so vibrations are transmitted more efficiently. In contrast, sound travels slower in liquids and slowest in gases. It cannot travel through a vacuum because there are no particles to carry the vibrations.