Practice Library
All MCQs
Browse exam-wise, subject-wise, and country-wise MCQs with explanations.
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Correct Answer: B. A covalent bond forms through sharing electron density between atoms
Explanation:
Covalent bonding arises from shared electron density, commonly between nonmetal atoms.
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Correct Answer: A. Across a period, effective nuclear charge generally increases and atomic radius tends to decrease
Explanation:
Across a period, increasing nuclear charge with similar shielding pulls valence electrons closer.
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Correct Answer: D. Increasing pressure shifts a gaseous equilibrium toward the side with fewer gas moles
Explanation:
A pressure increase favours the side occupying less gaseous volume; a catalyst changes rate, not equilibrium position.
Correct Answer: 2
Explanation:
pH=−log₁₀[H⁺]=−log₁₀(1e-02)=2.0.
Correct Answer: 0.667
Explanation:
M=n/V=2/3=0.667 mol/L.
Correct Answer: 40
Explanation:
Use mass = amount × molar mass. Therefore mass = 2 × 20 = 40 g.
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Correct Answer: C. Heritable traits that improve reproductive success can become more common across generations
Explanation:
Natural selection changes population trait frequencies when heritable variation affects reproductive success.
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Correct Answer: C. Aerobic respiration transfers energy from nutrients to ATP using electron carriers and oxygen as final acceptor
Explanation:
Aerobic respiration uses glycolysis, the citric acid cycle and oxidative phosphorylation to make ATP.
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Correct Answer: B. Light reactions generate ATP and reducing power used in carbon fixation
Explanation:
Light reactions provide ATP and NADPH, while the Calvin cycle fixes carbon into organic molecules.
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Correct Answer: B. Enzymes lower activation energy without being consumed by the reaction
Explanation:
Enzymes catalyse reactions by lowering activation energy; conditions influence their structure and rate.
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Correct Answer: D. Each new DNA molecule contains one parental strand and one newly synthesised strand
Explanation:
DNA replication is semiconservative and uses complementary base pairing.
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Correct Answer: B. Meiosis reduces chromosome number and creates variation through independent assortment and recombination
Explanation:
Meiosis forms haploid cells and generates variation through chromosome segregation and recombination.
