Explanation: Proteins are complex organic compounds composed of smaller units called amino acids. Each amino acid contains an amino group (–NH₂), which contributes nitrogen to the molecular structure. This makes nitrogen an essential element in all proteins. Carbohydrates and fats lack nitrogen, while only some vitamins contain it.

Biogas is a source of non-conventional (renewable) energy. It is produced through the anaerobic decomposition of organic waste materials such as animal dung, crop residues, and kitchen waste. Biogas mainly contains methane (CH₄) and is used as a clean fuel for cooking, lighting, and even power generation. It helps reduce dependence on fossil fuels and minimizes environmental pollution.

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• Firewood: A traditional biomass fuel, not classified as a modern non-conventional source.
• Diesel: A conventional fossil fuel derived from crude oil.
• Petrol: Another conventional fossil fuel obtained from petroleum refining.

Explanation: Vitamin K plays a crucial role in the blood clotting process. It helps the liver synthesize prothrombin and other clotting factors required to stop bleeding when injuries occur. Deficiency of Vitamin K can lead to excessive bleeding and delayed clot formation. Green leafy vegetables, broccoli, spinach, and intestinal bacteria are major natural sources of this vitamin.

Explanation: The term "Ozone hole" does not mean an actual hole but refers to a significant decrease in the thickness of the ozone layer in the Earth's stratosphere. This thinning occurs mainly over the Antarctic region during spring (September–November) due to chemical reactions involving chlorofluorocarbons (CFCs) and other ozone-depleting substances. These chemicals release chlorine and bromine atoms, which destroy ozone (O₃) molecules. The thinning allows more harmful ultraviolet (UV) radiation to reach the Earth's surface, causing health and environmental hazards.

Explanation: Measles is a highly contagious viral disease caused by the measles virus (a member of the Paramyxovirus group). It spreads through droplets released when an infected person coughs or sneezes. Symptoms include fever, cough, rash, and watery eyes. Other diseases listed — scurvy, asthma, and diabetes — are non-communicable as they do not spread from person to person.

Explanation: Aerosols (such as those used in spray cans, refrigerants, and air conditioners) often contain chlorofluorocarbons (CFCs) and other halogen compounds. These chemicals rise to the stratosphere, where ultraviolet (UV) radiation breaks them down, releasing chlorine atoms. Each chlorine atom can destroy thousands of ozone (O₃) molecules, leading to ozone layer depletion. The thinning of the ozone layer allows more harmful UV rays to reach Earth, increasing the risk of skin cancer, eye damage, and affecting ecosystems.

Explanation: 1 Gigabyte (GB) is equal to 1024 Megabytes (MB). Computer memory and storage are measured in powers of 2 (binary system), where 1 KB = 1024 bytes, 1 MB = 1024 KB, and 1 GB = 1024 MB.

The Air Quality Index (AQI) is a numerical scale used to measure and report the quality of air in a particular area. It primarily indicates the level of air pollution and its potential impact on human health. The AQI is calculated based on concentrations of key air pollutants — including ozone (O₃), particulate matter (PM₂.₅ and PM₁₀), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and carbon monoxide (CO). Higher AQI values indicate poorer air quality and greater health risks.

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