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: In 1643, Italian scientist Evangelista Torricelli invented the barometer, an instrument used to measure atmospheric pressure. His mercury barometer demonstrated that air has weight and that atmospheric pressure can support a column of mercury in a glass tube.

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: 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: Malaria is not caused by a virus; it is caused by a protozoan parasite of the genus Plasmodium. The disease spreads through the bite of an infected female Anopheles mosquito. The parasite enters the human bloodstream, infects liver cells, and then red blood cells, leading to recurring fever, chills, and anemia. In contrast, Smallpox, AIDS, and Flu are all viral diseases caused by the Variola virus, HIV, and Influenza virus respectively.

Explanation: The diseases Cholera, Tuberculosis, and Typhoid are all caused by bacteria, whereas Smallpox is caused by a virus (Variola virus). Bacterial diseases are typically treated with antibiotics, while viral diseases require vaccines or antiviral drugs. Cholera spreads through contaminated water, Typhoid through food and water, and Tuberculosis through droplets from infected individuals.

Explanation: The term LASER stands for Light Amplification by Stimulated Emission of Radiation. A laser produces a highly coherent, monochromatic, and intense beam of light by amplifying light through the process of stimulated emission. In this process, atoms or molecules in an excited state emit photons in phase with incoming photons, resulting in a strong, directed beam. Lasers are widely used in medicine, communication, industry, defense, and scientific research.

Explanation: The spectrophotometer measures bacterial growth by determining the optical density (OD) or turbidity of a culture. As bacteria multiply, the suspension becomes more turbid and absorbs more light. The absorbance value is proportional to the number of bacterial cells present.