Discussion
Which of the following statement is not correct?
Answer: B
The incorrect statement is Slaked lime slowly creates a layer of calcium nitrate on the walls during white washing.
The layer formed is calcium carbonate, not calcium nitrate. Slaked lime (calcium hydroxide) applied to the wall reacts slowly with carbon dioxide in the air:
\[ \mathrm{Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O} \]
which gives the shiny white finish a few days after whitewashing. Air supplies no nitrate for this reaction.
The other statements are correct. Calcium oxide (quick lime) reacts vigorously with water, releasing heat, to give slaked lime. Silver chloride turns grey in sunlight as it decomposes to silver and chlorine, which is why it is used in black and white photography. Decomposition reactions need energy, as heat, light or electricity, to break the reactants down.
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