Explanation: Gerontology is the branch of medical and biological science that deals with the study of aging and the diseases and problems specific to old age. It focuses on understanding the physical, mental, and social changes that occur in elderly individuals, as well as methods to promote healthy aging. Gerontology includes aspects of geriatrics, which specifically involves the medical care and treatment of elderly patients.

Swine Flu is caused by the H₁N₁ virus, a subtype of the Influenza A virus. It primarily affects the respiratory system and is transmitted from person to person through droplets from coughs or sneezes. Symptoms include fever, cough, sore throat, body aches, and fatigue. The H₁N₁ pandemic in 2009 was declared a global health emergency by the World Health Organization (WHO).

Other options (for context)

• Dengue: Caused by the Dengue virus, transmitted by Aedes mosquitoes.
• AIDS: Caused by the HIV (Human Immunodeficiency Virus), not H₁N₁.
• Bird flu: Caused by the H5N1 virus, not H₁N₁.

Explanation: The tusks of elephants are actually modified second upper incisors. They are made primarily of dentine, commonly known as ivory, and covered by a thin layer of enamel at the tip (which wears off with time). Tusks grow continuously throughout the elephant’s life and are used for digging, lifting objects, stripping bark, defense, and dominance displays.

Note: Both male and female African elephants have tusks, whereas in Asian elephants, tusks are generally present only in males.

Composition: Tusks are composed of dentine (ivory) with fine concentric growth lines, and they grow from sockets in the skull.

Explanation: The permissible noise level in residential areas should not exceed 55 decibels (dB) during the daytime and 45 dB at night, as per the Central Pollution Control Board (CPCB) guidelines. Exposure to higher noise levels can lead to stress, disturbed sleep, and hearing impairment.

Explanation: The branch of science that deals with the study of the production, behavior, and effects of materials at very low temperatures is called Cryogenics. The word comes from the Greek words “kryos” meaning cold and “gen” meaning to produce. Cryogenics involves cooling substances to temperatures below −150°C (123 K). It has applications in liquefying gases (like oxygen and nitrogen), cryopreservation of biological samples, superconductivity research, and rocket fuel storage (e.g., liquid hydrogen and oxygen).

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.

Explanation: Heavy water is chemically known as Deuterium oxide (D₂O). It is similar to ordinary water (H₂O), but the hydrogen atoms are replaced by deuterium — a heavier isotope of hydrogen containing one proton and one neutron. Heavy water is not suitable for drinking but is used as a moderator and coolant in nuclear reactors because it slows down neutrons, allowing a controlled nuclear fission reaction. It is also used in scientific research and isotope studies.

Explanation: The troposphere is the lowest layer of the Earth's atmosphere and is closest to the Earth's surface. It extends up to about 8–15 km from the surface, depending on latitude and season. This layer contains about 75% of the total atmospheric mass and almost all the water vapor and weather phenomena such as clouds, rain, and storms occur here. The temperature decreases with increasing altitude in this layer. The boundary between the troposphere and the stratosphere is known as the tropopause.

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).