The metal that cannot obtained by electrolysis of an aqueous solution of its salts is `:`

Options

A. ` Ag`
B. `Ca`
C. `Cu`
D. `Cr`

Answer

B

Explanation

Higher the position of element in the electrochemical series, more difficult is the reduction of its cation. Thus. Among all the given elements, only calcium on electrolysis yields ` H_2` gas at cathode wile other yields pure metals at cathode . In case of ` Ca^(2+)` ion, water is reduced in preference to calcimum.
For Cr At cathode , `Cr^(3+) + 3e^(-) rarr Cr`
For Ag At cathode , `Ag^+ + e^- rarr Ag`
For Cu At cathode, `Cu^(2+) + 2 e^(-) rarr Cu`
For `Ca^(2+)` At cathode, `H_2 O +e^- rarr 1/2 H_2 + OH^(-)`.