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.

Bioremediation is the process by which living organisms — mainly microbes, fungi, or plants — are used to remove or neutralize contaminants, pollutants, or toxins from soil, water, or air. These organisms break down harmful substances into less toxic or non-toxic forms, helping to clean up polluted environments naturally. It is an eco-friendly and cost-effective method for environmental restoration.

Other options (for context)

• Biotechnology: A broader field involving the use of living systems for industrial, agricultural, or medical purposes.
• Biodegradation: The natural breakdown of organic materials by microorganisms, but not necessarily aimed at pollution cleanup.
• Biomagnification: The accumulation of toxic substances in the food chain, opposite of pollution removal.

The Big Bang Theory explains the origin of the Universe. According to this theory, the universe began about 13.8 billion years ago from an extremely hot and dense state that expanded rapidly in all directions. This expansion continues even today, leading to the formation of galaxies, stars, planets, and other cosmic structures. The discovery of the cosmic microwave background radiation provides strong evidence supporting the Big Bang Theory.

Other options (for context)

• Origin of Sun: Explained by the Nebular Hypothesis, not the Big Bang Theory.
• Laws of Chemistry: Studied under physical and inorganic chemistry, unrelated to cosmology.
• Laws of History: Concern human civilizations, not the universe’s formation.

Explanation: Water shows an unusual property known as anomalous expansion. Its density is maximum at 4°C. When cooled from higher temperatures, water contracts till 4°C, becoming denser. Below 4°C, it expands instead of contracting, so its density decreases. This property allows ice to float and prevents water bodies from freezing solid, protecting aquatic life during winters.

Explanation: The pale yellow color of normal human urine is due to the presence of a pigment called Urochrome. It is produced from the breakdown of hemoglobin in red blood cells. The intensity of the color depends on the concentration of the urine — darker yellow indicates concentrated urine, while very pale or colorless urine suggests dilution due to high water intake.

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: Hardware refers to the physical components of a computer that can be seen and touched, such as the monitor, keyboard, mouse, CPU, and printer. In contrast, software consists of programs and instructions that control the hardware and perform tasks.

Explanation: The thyroid gland is located in the neck region, just below the larynx (voice box) and in front of the trachea (windpipe). It is a butterfly-shaped endocrine gland that secretes the hormones thyroxine (T₄) and triiodothyronine (T₃). These hormones regulate metabolism, growth, and energy production in the body. The thyroid also produces calcitonin, which helps control calcium levels in the blood. Iodine is essential for the synthesis of thyroid hormones.

Explanation: Saliva, secreted by the salivary glands, begins the process of carbohydrate digestion in the mouth. It contains the enzyme salivary amylase (also known as ptyalin), which catalyzes the breakdown of starch (polysaccharide) into maltose (disaccharide). This is the first step in digestion, and it occurs while food is chewed and mixed with saliva before being swallowed.

Chemical Reaction:

Starch → (Salivary amylase) → Maltose

Thus, saliva plays an essential role in the digestion of carbohydrates, making the food slightly sweet when chewed for a longer time.

Explanation: The blue colour of the sky is due to the scattering of sunlight by molecules and small particles in the Earth's atmosphere. Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (red and yellow). Since our eyes are more sensitive to blue light, the sky appears blue.