Question

Which among the following statements is /are true? Exposure of silver chloride to sunlight for a long duration turns grey due to.
(i) The formation of silver by decomposition of silver chloride.
(ii) Sublimation of silver chloride.
(iii) Decomposition of chlorine gas from silver chloride.
(iv)Oxidation of silver chloride.
A) (i) only.
B) (i) and (iii).
C) (ii) and (iii).
D) (iv) only.

Answer 1

We know that the decomposition reaction in reactants broken down to simpler substances by absorbing energy from photons is defined as a photolytic decomposition reaction. The decomposition of ozone is a suitable example of a photolytic decomposition reaction.
${O_3} + h\gamma \xrightarrow{{}}{O_2} + {O^.}$

Complete step by step answer:
First, we understand the decomposition reaction.
If a compound breaks down to two or more substances then it is a decomposition reaction. The general equation for the reaction is,
$AB\xrightarrow{{}}A + B$
Silver halides, especially Silver chloride undergo decomposition in presence of sunlight to produce silver metal and a halogen gas (chlorine or bromine gas).
$2AgCl\;(sunlight) \to 2Ag + C{l_2}$
White color of silver chloride changes to grey due to formation of silver metal.
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Therefore, the option A is correct.

Additional Information:

Now we discuss the difference between thermal and electrolytic decomposition reactions.
Thermal decomposition reaction: The decomposition reaction which is activated by the thermal energy is defined as a thermal decomposition reaction. The decomposition of Calcium Carbonate is a suitable example of a thermal decomposition reaction.
$CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2}$
Electrolytic decomposition reaction: The decomposition reaction which is activated by the electrical energy is defined as an electrolytic decomposition reaction. The electrolysis of water is a suitable example of an electrolytic decomposition reaction.
$2{H_2}O\xrightarrow{{}}2{H_2} + {O_2}$

Note:
We must remember that the silver chloride is stored in dark colored containers because silver chloride is photosensitive and it easily undergoes decomposition reaction in the presence of sunlight. Silver chloride is used as a photo chromic lens, which changes its color when exposed to sunlight. It is also used in electroplating and mirror polishing and it is commonly used as cathode in sea water activated batteries.