The Red Data Book contains information about endangered and threatened species of plants and animals. It is published by the International Union for Conservation of Nature (IUCN). The book categorizes species based on their risk of extinction, such as Critically Endangered, Endangered, Vulnerable, and Extinct. It serves as a global reference for monitoring biodiversity conservation and guiding environmental protection policies.

Other options (for context)

• All plant species: Incorrect — it includes only those plants that are endangered or threatened.
• All animal species: Incorrect — it covers only the endangered and vulnerable ones, not all animals.
• All extinct species: Incorrect — it includes species at risk of extinction, not only those already extinct.

Explanation: The colour of the sky without an atmosphere would appear black. On Earth, the sky looks blue because molecules in the atmosphere scatter sunlight — a phenomenon called Rayleigh scattering. Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (red). However, if there were no atmosphere to scatter sunlight, no light would be diffused in all directions, and the sky would appear completely dark or black, just as it does from the surface of the Moon or in outer space.

Explanation: A heavy stone appears lighter when immersed in water because of the upward pressure or buoyant force exerted by the water. This phenomenon is explained by Archimedes’ Principle, which states that a body immersed in a fluid experiences an upward force equal to the weight of the fluid displaced by it. The greater the volume of the object submerged, the greater the buoyant force acting on it. Hence, the stone seems lighter in water, even though its actual mass remains the same.

Adolf Gaston Eugen Fick, a German physiologist, invented the first successful contact lens in 1888. His design consisted of a glass lens that covered the entire eye, resting on the sclera (the white part of the eye). Though bulky and uncomfortable by today’s standards, it laid the foundation for modern soft and gas-permeable contact lenses used in vision correction and cosmetics.

Other options (for context)

• Enrico Fermi: Known for his work in nuclear physics and development of the first nuclear reactor.
• Sandford Fleming: Introduced the concept of standard time zones.
• Benoit Fourneyron: Invented the water turbine, not related to optics or vision correction.

Explanation: The onion is a modified underground stem called a bulb. It consists of a short, disc-like stem (the basal plate) surrounded by concentric fleshy leaf bases that store food. The roots emerge from the underside of the basal plate, and new shoots grow from the center. Thus, the onion bulb serves as a storage organ for nutrients and helps in vegetative propagation.

Explanation: Humans first develop a set of 20 milk teeth (also called deciduous or primary teeth) — 10 in the upper jaw and 10 in the lower jaw. These teeth start erupting around 6 months of age and are eventually replaced by 32 permanent teeth (including 4 wisdom teeth). Milk teeth help in early chewing, speaking, and maintaining space for permanent teeth.

Explanation: Teflon, also known as polytetrafluoroethylene (PTFE), is the polymer used in making non-stick kitchenware. It has a very low coefficient of friction and is resistant to heat and chemicals, which prevents food from sticking to cookware surfaces.

Explanation: The age of a tree is determined by counting the annual growth rings (also called annual rings) visible in a cross-section of its trunk. Each ring consists of a light band (spring wood) and a dark band (autumn wood), representing one year of growth. The study of these rings to determine a tree’s age and past climate conditions is known as dendrochronology.

Explanation: The Bhopal Gas Tragedy occurred on the night of December 2–3, 1984, at the Union Carbide pesticide plant in Bhopal, Madhya Pradesh (India). The disaster was caused by the accidental leakage of Methyl Isocyanate (MIC), a highly toxic and reactive gas used in pesticide manufacturing. The poisonous gas spread rapidly over the nearby populated areas, killing thousands of people and causing severe respiratory and neurological disorders. It is considered one of the world’s worst industrial disasters.

Explanation: The thyroid gland is located in the neck region, just below the larynx (voice box) and in front of the trachea (windpipe). It is a butterfly-shaped endocrine gland that secretes the hormones thyroxine (T₄) and triiodothyronine (T₃). These hormones regulate metabolism, growth, and energy production in the body. The thyroid also produces calcitonin, which helps control calcium levels in the blood. Iodine is essential for the synthesis of thyroid hormones.