Explanation: Vitamin A is essential for maintaining healthy vision, skin, and immune function. A deficiency of Vitamin A leads to night blindness (nyctalopia), a condition in which a person has difficulty seeing in dim light or at night. In severe cases, it can cause xerophthalmia (dryness of the cornea) and even blindness. Vitamin A is obtained from foods such as carrots, milk, butter, fish liver oil, and green leafy vegetables.

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: According to the Bureau of Indian Standards (BIS) – IS 10500:2012, the acceptable limit of total hardness in drinking water, expressed as CaCO₃, is 200 mg/l. The permissible limit in the absence of an alternate source is up to 600 mg/l. Excess hardness can cause scaling and affect the taste of water.

Explanation: Liquid Natural Gas (LNG) predominantly contains methane (CH₄) in liquid form. It is produced by cooling natural gas to about −162°C, which reduces its volume for easier storage and transportation. LNG is a clean fuel with high energy efficiency and low emissions.

Explanation: When a sound wave travels from one medium to another, its frequency remains unchanged. However, its wavelength and speed change depending on the properties of the new medium. The constant frequency ensures that the sound maintains the same pitch.

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: Normal human blood has a slightly alkaline pH of 7.35 to 7.45. This pH is maintained by buffer systems such as the bicarbonate buffer system and controlled by the lungs (CO₂ regulation) and kidneys (acid-base balance). A deviation from this range can be life-threatening — acidosis occurs if pH falls below 7.35, and alkalosis occurs if it rises above 7.45.

Explanation: Penicillin was discovered accidentally by Alexander Fleming in 1928 when he observed that a fungal mold, Penicillium notatum, inhibited the growth of Staphylococcus bacteria in his culture plates. Penicillin became the first antibiotic used to treat bacterial infections and saved millions of lives during World War II. Later, scientists like Howard Florey and Ernst Boris Chain developed methods for its large-scale production.

Explanation: VoIP (Voice over Internet Protocol) is a technology that allows users to make telephone calls over the Internet instead of traditional telephone lines. It converts voice signals into digital data packets and transmits them through computer networks, enabling cost-effective communication worldwide.

Explanation: Dakshin Gangotri is India’s first scientific research station established in Antarctica in 1983–84. It was set up by the Indian Antarctic Programme under the National Centre for Polar and Ocean Research (NCPOR). Located about 2,500 km from the South Pole, it served as a base for scientific studies related to glaciology, meteorology, and environmental sciences. Though it is now buried under ice and functions as a supply base, it marked India’s permanent presence in Antarctica. Later stations include Maitri (1989) and Bharati (2012).