Which of the following is a decomposition reaction used in black and white photography?
A. 2AgCl → 2Ag + Cl₂
B. 2H₂O → 2H₂ + O₂
C. 2AgBr → 2Ag + Br₂
D. CaCO₃ → CaO + CO₂
Answer: Option C
Solution (By JKSSB Mock Tests)
Silver bromide (AgBr) decomposes on exposure to light (photochemical decomposition) forming silver and bromine: 2AgBr(s) → 2Ag(s) + Br₂(g). This is used in photographic films to capture images. AgCl also light-sensitive but AgBr is primarily used. Calcium carbonate decomposition is thermal. Water electrolysis is electric decomposition.
Explanation:
Endothermic reactions absorb heat from the surroundings. The decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) requires continuous heating to proceed. Burning of gas, respiration, and the reaction of sodium with water are all exothermic reactions that release significant amounts of heat energy to the surroundings.
Explanation:
Catalysts lower activation energy, providing an easier pathway, thus increasing reaction rate. They do not affect equilibrium constant or get consumed.
Explanation:
According to Graham's law, the rate of diffusion is inversely proportional to the square root of molar mass. Hydrogen (H₂) has the lowest molar mass (2 g/mol) among the options (O₂=32, N₂=28, CO₂=44), so it will diffuse the fastest under identical conditions of temperature and pressure.
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