Practice questions without fighting the page.

<b>Correct answer: B - starch</b> <ul> <li>Key concept: Saliva contains <em>salivary amylase</em>, an enzyme that digests starch in the mouth.</li> <li>Process: Starch + H2O --<em>amylase</em>--> maltose (and glucose in small amounts).</li> <li>Other options: <ul><li>A fats: lipase acts mainly in the small intestine; saliva has minimal fat digestion.</li> <li>C proteins: proteases (like pepsin) start in the stomach, not saliva.</li> <li>D vitamins: vitamins are absorbed, not digested by saliva.</li></ul></li> </ul> <b>Exam tip:</b> Remember: mouth digestion mainly carbohydrates via amylase.

<b>Correct answer: C</b> <ul> <li><b>Why it’s correct:</b> Ocean thermal energy relies on the <u>temperature difference</u> between warm surface water and cold deep water to drive work (OTEC).</li> <li><b>Key concept:</b> Thermodynamic gradient enables heat transfer to power a cycle (often a Rankine-like cycle) using two temperature reservoirs.</li> <li><b>Simple formula (conceptual):</b> Q = m·c·ΔT for heat transfer between layers; larger ΔT yields more energy.</li> <li><b>Exam tip:</b> Remember: not tides, pressure, or waves—it's the <u>thermal gradient</u> with depth.</li> <li><b>Why others are incorrect:</b> A: tides are gravitational; B: pressure differences are not the energy source for OTEC; D: waves store energy, not the basic source for OTEC.</li> </ul>

<b>Correct option: A</b><br> <b>Answer:</b> Cadmium <br><br> <ul> <li><b>Reason:</b> Cadmium is a toxic heavy metal that damages the kidneys, especially the renal tubules, leading to nephrotoxicity and kidney disease.</li> <li><b>Key concept:</b> Heavy metal-induced nephrotoxicity; Cd accumulates in proximal tubule cells causing functional impairment.</li> <li><b>Note on others:</b> Iron, Cobalt, and Carbon are not primarily linked to causing chronic kidney disease in this context.</li> <li><b>Exam tip:</b> Remember common nephrotoxic metals—cadmium is a classic culprit for kidney damage.</li> </ul>

<b>Correct answer: B. Dermatitis</b> <ul> <li><b>Reason:</b> Nickel exposure commonly causes allergic contact dermatitis (a type IV hypersensitivity). It leads to skin itch, redness, and rashes at the contact site.</li> <li><b>Key concept:</b> Nickel allergy is a classic example of cell-mediated (T-cell) immune reaction to a metal.</li> <li><b>Quick note on others:</b> Itai-Itai is due to cadmium poisoning; learning disabilities and asthma are not specific to nickel exposure.</li> <li><b>Exam tip:</b> Remember metals often cause contact dermatitis rather than systemic diseases.</li> </ul>

<b>Correct answer: D</b> — Chickungunya <ul> <li><b>Key concept:</b> Chickungunya is caused by a virus (Chikungunya virus), not bacteria.</li> <li><b>Other options:</b> Cholera (bacteria Vibrio cholerae), Typhoid (bacteria Salmonella typhi), Tuberculosis (bacteria Mycobacterium tuberculosis).</li> <li><b>Why viral, not bacterial:</b> Viruses are smaller and require host cells to replicate; diseases like chikungunya spread via Aedes mosquitoes as a vector.</li> </ul> <b>Exam tip:</b> Remember “Chikungunya = viral, mosquito-borne” to distinguish from bacterial, water- or food-borne diseases.

<b>Correct option: B</b> <ul> <li>Vinegar is a solution of <b>diluted acetic acid</b> (CH3COOH) in water along with trace compounds that give its smell and taste.</li> <li>Key concept: acid in solution; acetic acid is a weak acid, giving acidic pH in dilute form.</li> <li>Why others are incorrect: A) citric acid is in citrus fruits, not vinegar; C) hydrochloric acid is strong and not used in vinegar; D) oxalic acid is a different acid not typical in vinegar.</li> <li>Exam tip: remember “vinegar = acetic acid” due to its distinctive sour taste and usage in pickling.</li> </ul>

<b>Correct answer: C</b> <ul> <li>Electrons are negatively charged and are present in the orbits.</li> </ul> <p><b>Reason:</b> An atom has a dense nucleus (protons positively charged; neutrons neutral). Electrons, negatively charged, occupy surrounding regions called orbits or orbitals. The total mass mainly comes from the nucleus, not the orbits. The electric charge balance is q(electron) = -e.</p> <ul> <li><b>Why others are wrong:</b></li> <li>A: Protons are positively charged and in the nucleus.</li> <li>B: Electrons are not in the nucleus and are negative.</li> <li>D: Mass is concentrated in the nucleus, not distributed in orbits.</li> </ul> <p><b>Exam tip:</b> Remember negative charges orbit a positive nucleus.</p>

<ul> <li><b>Correct option: B</b> — Noise</li> <li><b>Reason:</b> A green muffler is a noise-reduction device attached to vehicles or machinery to lower sound levels, thus tackling noise pollution.</li> <li><b>Key concept:</b> Acoustic damping and energy dissipation reduce sound intensity emitted by engines or machinery.</li> <li><b>Formula/logic (brief):</b> Sound reduction involves decreased sound intensity, often measured in decibels (dB); a muffler reduces dB levels.</li> <li><b>Exam tip:</b> If the option mentions pollution types, choose the one related to sound for devices labeled “muffler.”</li> <li><b>Why others are incorrect:</b> It does not primarily prevent air, soil, or water pollution.</li> </ul>

A banana is an elongated, edible fruit, botanically a berry, produced by several kinds of large herbaceous flowering plants in the genus Musa.

<b>Explanation</b> <ul> <li>In ground frame, rain falls vertically. The car moves forward with speed v, so relative to the car the rain has a horizontal component toward the back: v_r = (0, -u) − (v, 0) = (−v, −u).</li> <li>Thus rain appears to come from the front and hits the front windshield (not the rear).</li> </ul> <b>Key concept:</b> Relative velocity between rain and car determines impact direction. If rain is vertical in ground frame, moving forward car makes rain strike the front screen. <b>Exam tip:</b> Always use relative velocity v_rain+car to predict impact direction.