Explanation: Sound waves in air are longitudinal waves, meaning the particles of the medium vibrate back and forth in the same direction as the wave travels. These waves require a material medium (like air, water, or solids) for propagation and cannot travel through a vacuum.

Explanation: The transmission of light through optical fibres is based on the principle of Total Internal Reflection (TIR). When light travels from a denser medium (core of the fibre) to a rarer medium (cladding) and strikes the interface at an angle greater than the critical angle, it gets completely reflected back into the core instead of refracting out. This continuous internal reflection allows light to travel long distances through the fibre with minimal loss, even when the fibre is bent. Optical fibres are widely used in telecommunication, internet data transfer, and medical endoscopy.

Explanation: Web pages are written using HTML (HyperText Markup Language). It is the standard language used to create and structure content on the web by defining elements such as headings, paragraphs, links, images, and tables.

Explanation: A microscope uses a system of convex lenses to magnify very small objects. Convex lenses, also known as converging lenses, bend light rays inward to a focal point, creating an enlarged and clear image of the specimen. A compound microscope typically contains two sets of convex lenses — the objective lens (near the specimen) and the eyepiece lens (near the observer’s eye). The objective lens forms a real, inverted, and magnified image, which is then further magnified by the eyepiece to produce a large virtual image.

Sputnik I was the first artificial satellite to orbit the Earth. It was launched by the Soviet Union on October 4, 1957. The successful launch of Sputnik I marked the beginning of the space age and initiated the space race between the USA and the USSR.

• Explorer I: First U.S. satellite, launched in 1958.
• Vanguard I: A U.S. satellite launched later in 1958.
• Discoverer I: Part of an American reconnaissance satellite program (1959).

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.

Explanation: An artery is a large blood vessel that carries blood away from the heart to various parts of the body. Arteries have thick, elastic walls to withstand high pressure. In contrast, veins carry blood toward the heart, and capillaries are tiny vessels that connect arteries and veins.

The Green Revolution is associated with Agriculture. It refers to the period during the 1960s–70s when new technologies like high-yield variety (HYV) seeds, fertilizers, irrigation, and pesticides were introduced to boost food grain production, especially wheat and rice. It helped India achieve self-sufficiency in food production.

• Sericulture: Rearing of silkworms for silk.
• Fishery: Cultivation and harvesting of fish.
• Cultivation of bees: Known as apiculture, for honey production.

Dynamite was invented by Alfred Nobel in 1867. He was a Swedish chemist, engineer, and industrialist who discovered that nitroglycerin could be stabilized by mixing it with an absorbent material like diatomaceous earth, making it safer to handle and transport. This invention revolutionized the mining and construction industries. In his later years, Alfred Nobel established the Nobel Prizes using the wealth he accumulated from his inventions.

Other options (for context)

• J. B. Dunlop: Invented the pneumatic rubber tyre.
• James Simons: A mathematician and hedge fund manager, not an inventor.
• Peter Hargreaves: Not related to any major scientific invention; possibly confused with James Hargreaves, who invented the Spinning Jenny.

Explanation: Mercury is used in clinical thermometers mainly because it is a good conductor of heat, allowing it to quickly reach the temperature of the patient’s body. Additionally, it has a uniform rate of expansion, remains liquid over a wide temperature range, and has a shiny appearance for easy visibility of the reading.