General Science MCQ Practice

• The thyroid is the largest pure endocrine gland, located in the neck and producing hormones T3/T4 and calcitonin.
• Other options are smaller glands: parathyroid, adrenal, and pituitary.
• Key concept: endocrine glands secrete hormones directly into the blood; thyroid mass makes it the largest among endocrine organs.
• Tip: Remember “largest endocrine gland” = thyroid—distinct from the liver (not purely endocrine) in size.

• Why it’s correct: Normal human blood pH is tightly regulated around 7.4 (slightly basic). The body maintains this via buffering systems and organ regulation.

• Why: Coriander leaves (cilantro) are used fresh for aroma and garnish, while the dried fruits (seeds) are widely used as spice. This covers the edible parts: leaves and dried fruits.
• Key concept: Different plant parts have different culinary uses; coriander seeds are dried fruits, not berries or roots.
• Tip: If a question asks “useful parts,” think of what is commonly used in cooking as the edible leafy part and the dried fruit/seed part.
• Why others are incorrect: Roots are not commonly used; flowers are not the main usable part; dried fruits are correct in combination with leaves.

• Reason: Monazite sand is rich in phosphate minerals containing rare earths and thorium, with thorium-232 commonly present as an impurity/ constituent.
• Key concept: Thorium is a fertile material used in nuclear energy; monazite concentrates are a primary ore source.
• Quick note on options: Potassium and sodium are common alkali minerals not characteristic of monazite; uranium can be present but is not the defining mineral of monazite sands.
• Exam tip: If asked about monazite composition, prioritize thorium content over alkali elements.

• Explanation: Edward Jenner developed the first vaccine for smallpox using material from cowpox lesions to induce immunity. This concept—vaccination—uses a harmless or weaker pathogen to train the immune system.
• Key concept: Immunization by exposing the body to a less dangerous version of a pathogen to build protection.
• Why others are incorrect: Banting (insulin), Fleming (penicillin), Pasteur advanced vaccines but did not invent the smallpox vaccine.
• Exam tip: Remember “Jenner’s cowpox” as the origin of vaccination.

• Explanation: Most aquatic organisms require dissolved oxygen (DO) in the range of 4–6 mg/L for survival and normal metabolism.
• Key concept: DO levels indicate water quality; too low causes stress or death, too high is unnecessary for biological needs.
• Reasoning: DO concentration is measured in mg/L; 4–6 mg/L supports respiration and aerobic metabolism.
• Exam tip: When options are ranges, choose the range that includes the commonly cited normal DO for freshwater fisheries.
• Why others are incorrect: 2–4 is often stressed/near-anaerobic; 8–10 and 12–16 exceed typical requirements and may indicate supersaturation or different contexts.

• Reason: Iodoform (CHI3) releases iodine, giving germicidal action; it has historically been used to disinfect wounds and surfaces.
• Key concept: Halogenated compounds with iodine provide antiseptic properties via disruption of microbial proteins.
• Formula/logic (brief): CHI3 → iodine source; iodine kills microbes.
• Exam tip: Remember common antiseptics include iodine-based agents; antipyretics relieve fever, analgesics relieve pain, and anaesthetics block sensation.
• Why others are incorrect: A reduces fever, B relieves pain, D blocks sensation; none describe antiseptic use.

• Why: White lung disease (silicosis) occurs from inhaling crystalline silica dust, common in cement production.
• Key concept: Silica particles cause fibrotic nodules in lungs, reducing ventilation and gas exchange.
• Numerical logic: Dose and duration of exposure correlate with disease severity; higher exposure over time increases risk.
• Exam tip: Note industries with silica dust—cement, foundries—and emphasize protective measures.

Correct option: C

• Explanation: Gypsum (CaSO4·2H2O) is added to Portland cement to prevent rapid (flash) setting by delaying the hydration of tricalcium aluminate (C3A). This keeps the mix workable for a reasonable time.
• Key concept: Setting delay through chemical inhibitors in cement hydration; gypsum acts as a regulator of aluminate hydration.
• Exam tip: If a question asks about preventing rapid setting, think of additives like gypsum in cement.
• Why others are incorrect: A: gypsum does not primarily increase early strength; B: it prevents rapid setting, not accelerates; D: cost reduction is not the main purpose.

• Reason: Liquid hydrogen (fuel) + liquid oxygen (oxidizer) form a highly energetic reaction: 2H2 + O2 → 2H2O, releasing ~286 kJ per mole of H2. This high specific impulse makes LH2/LOX ideal as a rocket propellant.
• A (liquid hydrogen + liquid nitrogen) is not feasible; nitrogen is not a good oxidizer and would not support combustion.
• B (liquid oxygen + liquid argon) uses a noble gas (argon) as oxidizer partner; argon is inert and does not support combustion.
• C (liquid nitrogen + liquid oxygen) lacks a proper fuel; nitrogen is inert at rocket-operating conditions.

Exam tip: True rocket propellants require a fuel and an effective oxidizer; inert or non-reactive partners cannot support the combustion needed for thrust.