Indian Navy 10+2 B.Tech Cadet Chemical Reactions and Equations — practice questions

Explore 2 free Chemical Reactions and Equations questions in Indian Navy 10+2 B.Tech Cadet Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Chemical Reactions and Equations questions and exercises with answers

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Which reaction does NOT need heat to proceed?Read the answer and worked solution →Silver objects turn black on long exposure to air mainly because:Read the answer and worked solution →

Worked practice questions

Which reaction does NOT need heat to proceed?

2 H₂O → 2 H₂ + O₂
2 AgCl → 2 Ag + Cl₂
CaO + H₂O → Ca(OH)₂
CaCO₃ → CaO + CO₂

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Correct answer: C. CaO + H₂O → Ca(OH)₂

Slaking of lime is a vigorous combination that releases heat rather than needing it. The other three are decompositions that require heat, electricity, or sunlight.

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Silver objects turn black on long exposure to air mainly because:

Ag combines with H₂S to form Ag₂S
Ag combines with O₂ to form Ag₂O
Ag reacts with CO₂ to form Ag₂CO₃
Ag dissolves in moisture slowly

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Correct answer: A. Ag combines with H₂S to form Ag₂S

Atmospheric hydrogen sulfide reacts with silver to form black silver sulfide (Ag₂S). This is the corrosion mechanism for silver — not simple oxidation by O₂.