Answer is B
The answer to the question is Option (b) because in the Electrochemical Series Ca is placed above H so it cannot be displace the metal in its aqueous solution. All the other metals given in the options are present are be placed below H thus can be easily obtained via electrolysis.
The electrolysis method is used to obtained the elements which has lower reactivity than hydrogen, because in that setup ,the hydrogen will be liberated at the anode and the metal will be obtained at cathode.
So,in above the Ca is more reactive than hydrogen. So it can't be obtained by electrolysis.
Hope you will clearly understand this.