Explanation: The angle of friction and the angle of repose are equal to each other. The angle of friction is the angle made by the resultant of the limiting friction and normal reaction with the normal force, while the angle of repose is the maximum angle of an inclined plane at which an object just begins to slide. Both represent the same physical condition of impending motion.

Explanation: Bryology is the branch of botany that deals with the study of bryophytes, which include mosses and liverworts. These are small, non-vascular plants that typically grow in moist and shady environments.

Explanation: Nucleons are the particles that make up the nucleus of an atom — namely, protons and neutrons. A positron is not a nucleon; it is the antiparticle of the electron, having the same mass as an electron but a positive charge, and exists outside the nucleus.

Explanation: PARAM 8000 is India's first supercomputer, developed in 1991 by the Centre for Development of Advanced Computing (C-DAC) under the leadership of Dr. Vijay Bhatkar. It marked India’s entry into high-performance computing and was capable of 1 GigaFLOP (one billion calculations per second).

Explanation: Human blood is maintained at a slightly alkaline pH of 7.4 (range 7.35–7.45). This balance is vital for the proper functioning of enzymes and biochemical reactions in the body. The buffer systems in blood — primarily the bicarbonate buffer system (H₂CO₃ / HCO₃⁻) — help maintain this stable pH. A small deviation from this range can lead to severe physiological disturbances.

Imbalances:

• Acidosis: pH below 7.35 — causes drowsiness, confusion, and respiratory distress.
• Alkalosis: pH above 7.45 — causes muscle twitching, irritability, and convulsions.

Explanation: Fish respire through specialized organs called gills, located on either side of their head. Gills contain thin filaments with a large surface area and rich blood supply that allow exchange of gases. When water passes over the gill membranes, oxygen diffuses into the blood and carbon dioxide diffuses out. This process enables aquatic respiration and supports survival underwater.

Graphite is used in pencils. It is a soft form of carbon that leaves a dark mark on paper due to its layered structure, where carbon atoms are arranged in sheets that slide easily over each other. Though commonly called “lead,” pencils actually contain graphite mixed with clay to adjust hardness.

• Silicon: Used in electronics, not pencils.
• Charcoal: Used in art drawing but not regular pencils.
• Phosphorous: Used in safety matches and fertilizers, not pencils.

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.