Practice questions without fighting the page.

<b>Correct option: D</b> <ul> <li><b>Argon</b> is an inert gas, belonging to the noble gases group with a complete outer electron shell, making it chemically very unreactive under normal conditions.</li> <li>Key concept: inert gases have stable electron configurations (noble gas configuration) and form few or no compounds.</li> <li>Why others are not inert: <ul> <li>Hydrogen can react to form many compounds (H2, acids, hydrocarbons).</li> <li>Nitrogen, though relatively unreactive, forms N2 and can react under certain conditions (fertilizers, explosives).</li> <li>Oxygen is highly reactive and supports combustion.</li> </ul> </li> <li>Exam tip: recall “noble gases” (He, Ne, Ar, Kr, Xe, Rn) as the truly inert ones.</li> </ul>

<b>Answer: A) Poor night vision</b> <ul> <li><b>Key concept:</b> Vitamin A is essential for rhodopsin in retina. Deficiency causes nyctalopia (night blindness).</li> <li><b>Why correct:</b> Lack of Vitamin A impairs vision in low light, leading to poor night vision.</li> <li>

On 2–3 December, 1984 at the Union Carbide India Limited (UCIL) pesticide plant.

<b>Correct answer: A. Cadmium</b> <ul> <li><b>Key concept:</b> Itai-Itai disease is caused by chronic cadmium poisoning, leading to severe kidney damage and softening of bones.</li> <li><b>Why correct:</b> Cadmium accumulates in the body from contaminated water/food and affects kidneys and bones, producing the characteristic pain and weakness.</li> <li><b>Other options:</b> <ul> <li>Nickel, chromium, mercury do not cause Itai-Itai disease.</li> </ul> </li> <li><b>Tip:</b> Remember cadmium toxicity is linked to renal + skeletal damage.</li> </ul>

<b>Answer Explanation</b> <ul> <li><b>Correct option: C</b> - Air Quality Index measures levels of ozone (O3) among pollutants in the selected area to assess air quality.</li> <li><b>Key concept:</b> AQI combines pollutant concentrations into a single scale to indicate health risk from pollutants including ground-level ozone.</li> <li><b>Why others are incorrect:</b> <ul> <li>Option A: Not about sound pollution.</li> <li>Option B: It does not focus only on sulphur; it covers multiple pollutants.</li> <li>Option D: It does not assess colour of air.</li> </ul> </li> <li><b>Tip for exam</b>: Remember AQI = function of concentrations f(pollutants) mapped to a standard scale.</li> </ul>

<b>Correct option: B</b> — <b>Pace-maker</b> <ul> <li>The SA node generates rhythmic electrical impulses that set the heart rate, acting as the natural “pacemaker.”</li> <li>Key concept: automaticity and rhythmic rhythm generation in the sinoatrial node.</li> <li>Why others are wrong: Autoregulator, Time controller, and Beat regulator are not standard terms for initiating heartbeats.</li> <li>Exam tip: Remember “SA node = pace-maker” as the primary initiator of heartbeat. No formula needed.</li> </ul>

<b>Correct option: A</b> <ul> <li><b>Explanation:</b> Antibodies are immune system proteins that recognize and neutralize pathogens, forming the body’s defense against diseases.</li> <li><b>Key concept:</b> antigen–antibody interaction; antibodies are produced by B cells.</li> <li><b>Why others are incorrect:</b> DNA/RNA are genetic material; enzymes catalyze reactions, not direct pathogen defense.</li> <li><b>Exam tip:</b> remember “antibodies” are the specific immune proteins, not the genetic material or general catalysts.</li> </ul>