Explanation: Stars appear to twinkle at night due to the refraction of light by the Earth's atmosphere. As starlight passes through different layers of air with varying densities, its path bends continuously, causing the light’s intensity and position to appear to change, creating the twinkling effect.

Explanation: Chlorofluorocarbons (CFCs) are the gases responsible for the depletion of the ozone layer. When released into the atmosphere, CFCs break down under ultraviolet (UV) radiation, releasing chlorine atoms that destroy ozone molecules (O₃), leading to thinning of the ozone layer and increased UV radiation reaching the Earth.

Explanation: The sour taste of a lemon is due to the presence of citric acid. Citric acid is a weak organic acid found naturally in citrus fruits such as lemons, oranges, and limes. It gives them their characteristic tangy flavor and also acts as a natural preservative.

Explanation: The erythrocytes (RBCs) play a crucial role in the circulation of blood by carrying oxygen from the lungs to body tissues and returning carbon dioxide for exhalation. They contain hemoglobin, which binds oxygen and maintains the red color of blood. Circulation itself is driven by the heart and supported by these oxygen-carrying cells.

Explanation: The terms Dolby B and Dolby C refer to noise reduction circuits used in tape recorders and sound systems. These technologies reduce background hiss and unwanted noise during playback and recording, thereby improving the overall sound quality.

Tuberculosis (TB) is commonly known as the "White Plague". It earned this name because it causes extreme paleness and weight loss in affected individuals. Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis, primarily affecting the lungs but can also spread to other parts of the body. It spreads through airborne droplets when an infected person coughs or sneezes.

Other options (for context)

• Typhoid: Caused by Salmonella typhi, affects the intestine and causes high fever.
• Malaria: Caused by Plasmodium parasite transmitted through mosquito bites.
• Plague: Caused by Yersinia pestis, historically known as the “Black Death,” not the white plague.

Explanation: Bryology is the branch of botany that deals with the study of bryophytes, which include mosses and liverworts. These are small, non-vascular plants that typically grow in moist and shady environments.

Explanation: The S.I. unit of electric current is the Ampere (A). It is defined as the rate of flow of electric charge through a conductor. One ampere equals one coulomb of charge passing through a point in one second.

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.