Agniveer Army Science — practice by topic

Answer: C. Cicada, Froghopper and Pond skater are all INSECTS. (1) Cicada (Hemiptera: Cicadidae) is a true bug famous for the loud songs of males. (2) Froghopper (Hemiptera: Cercopidae) is the insect whose nymphs produce the protective 'spit' (cuckoo-spit) on plants. (3) Pond skater (Hemiptera: Gerridae) is the aquatic insect that walks on the water surface thanks to hydrophobic legs and surface tension. All three are members of the order Hemiptera (true bugs). None are birds, fish or reptiles. Source: syllabus Biology Ch 4 (Animal Kingdom) and standard entomology references.

Answer: A. Nitric oxide (NO) is the body's natural vasodilator. Nitric oxide is a free-radical signalling molecule produced in the body by endothelial cells lining blood vessels. It diffuses to the smooth muscle around vessels and triggers relaxation, causing vessels to dilate and blood flow to increase. The discovery of NO as a signalling molecule won the 1998 Nobel Prize in Physiology or Medicine (Furchgott, Ignarro, Murad). Drugs like nitroglycerin work by releasing NO to relieve angina. **Distractors fail:** (B) Nitrous oxide N2O is laughing gas, an anaesthetic, not a natural vasodilator. (C) Nitrogen dioxide NO2 is a toxic air pollutant. (D) Nitrogen pentoxide N2O5 is an unstable industrial intermediate, not biologically synthesised. Source: syllabus Biology / Nobel Prize 1998 citation.

Answer: D. The exhaust emission from a hydrogen Fuel Cell Electric Vehicle is WATER VAPOUR. In a hydrogen FCEV, hydrogen (H2) from the fuel tank combines with oxygen (O2) from the air at the fuel cell's catalyst surface. The electrochemical reaction is: 2 H2 + O2 -> 2 H2O + electricity. The only chemical product leaving the exhaust is water (released as vapour due to operating temperature). This zero-emission profile is the main environmental selling point of FCEVs over internal combustion engines. Distractors fail: (A) Hydrogen peroxide is not formed under normal fuel cell operation. (B) Hydronium (H3O+) is a transient species in the electrolyte membrane, not exhaust. (C) Oxygen is consumed, not emitted. Source: Ministry of New and Renewable Energy + IEA Hydrogen Technology Roadmap.