The metal that cannot be obtained by electrolysis of an aqueous solution of its salts is:
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The discharge potential of Ca is less than hydrogen, if aqueous solution is taken H2 will discharged first instead of Ca.
or
Deposition potential of Cu, Cr and Ag will be more than that of H2 and deposition potential of Ca will be less than that of H2.
Ca cannot be obtained by electrolysis.
(1)