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: The element hydrogen is common to all acids. Acids are substances that produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺) when dissolved in water. This property gives acids their characteristic sour taste, the ability to turn blue litmus paper red, and to react with bases to form salts and water. Examples include hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃)—all of which release hydrogen ions in aqueous solution.

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.

Other options (for context)

• 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.

Marble is not an element; it is a metamorphic rock composed primarily of calcium carbonate (CaCO₃). It forms when limestone is subjected to high pressure and temperature, causing recrystallization. Being a compound and mixture of minerals, marble does not consist of a single type of atom, unlike elements.

Other options (for context)

• Oxygen (O₂): A chemical element essential for respiration and combustion.
• Nitrogen (N₂): A chemical element that makes up about 78% of Earth’s atmosphere.
• Hydrogen (H₂): The lightest chemical element and the main component of stars.

Sound waves from a loudspeaker are produced by vibrations of its diaphragm. When an electric current passes through the speaker coil, it causes the diaphragm to move back and forth, creating compressions and rarefactions in the air. These pressure variations travel as sound waves to our ears.

• Frequency: Determines pitch but does not create sound.
• Pitch: A property of sound, not its cause.
• Amplitude: Determines loudness but not the origin of sound.

Explanation: Malaria and Trichomoniasis are both protozoan diseases, not bacterial. Malaria is caused by Plasmodium species (transmitted by female Anopheles mosquitoes), while Trichomoniasis is caused by Trichomonas vaginalis, a sexually transmitted protozoan infection. Unlike bacterial diseases, these are treated using antiprotozoal drugs rather than antibiotics.

The Green Muffler technique is used to control noise pollution. It involves planting dense rows of trees and shrubs around roads, industrial areas, and public places. The vegetation acts as a natural sound barrier by absorbing, deflecting, and refracting sound waves, thereby reducing the intensity of noise reaching nearby areas. Common plants used for green mufflers include Neem, Ashoka, Ficus, and Cassia.

Other options (for context)

• Air pollution: Controlled by measures like emission filters and afforestation, but not directly by green mufflers.
• Soil pollution: Managed by waste treatment and reduced chemical use, not vegetation barriers.
• Water pollution: Controlled by sewage treatment and reducing industrial discharge, not by plants as mufflers.

The Stockholm Convention is not associated with the reduction of greenhouse gases. It focuses on eliminating or restricting the production and use of persistent organic pollutants (POPs) — toxic chemicals that remain in the environment for long periods, such as DDT and PCBs. It does not directly address greenhouse gas emissions or climate change.

Other options (for context)

• Kigali Amendment to the Montreal Protocol: Aims to phase down the use of hydrofluorocarbons (HFCs), which are potent greenhouse gases used in refrigerants — hence it helps reduce global warming.
• Kyoto Protocol: An international treaty adopted in 1997 to reduce greenhouse gas emissions by developed countries, directly targeting climate change.

Explanation: The heart is enclosed in a double-layered protective membrane called the pericardium. The outer fibrous layer protects the heart and anchors it within the chest cavity, while the inner serous layer secretes pericardial fluid that reduces friction during heartbeats. This fluid-filled sac ensures smooth and cushioned movement of the heart as it contracts and relaxes continuously.

Explanation: Among the given particles, the proton is the heaviest. A proton is a positively charged subatomic particle found in the nucleus of an atom, with a mass of approximately 1.672 × 10⁻²⁷ kg. Although the neutron is slightly heavier than a proton, in most general questions like this one, protons are considered heavier in context when compared with electrons and neutrinos. Electrons are much lighter, with a mass about 1/1836 that of a proton, while neutrinos are nearly massless and electrically neutral.