Which one of the following metals could not be obtained on electrolysis of aqueous solution of its salts
Which one of the following metals could not be obtained on electrolysis of aqueous solution of its salts
$\mathrm{Ag}$
$\mathrm{Mg}$
$\mathrm{Cu}$
$\mathrm{Cr}$
Solution
The reduction potential of $\mathrm{Mg}$ is less than that of water $\left(\mathrm{E}^{0}=-0.83 \mathrm{~V}ight)$. Hence their ions in the aqueous solution cannot be reduced instead water will be reduced
$2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} ightarrow \mathrm{H}_{2}+2 \mathrm{OH}^{-}$