The correct option is
A x=4, y=2, z=4The unbalanced chemical equation is,
Cu(NH3)42+(aq)+S2O42−(aq)→SO32−(aq)+Cu(s)+NH3(aq)
Balance N and S atoms.
Cu(NH3)42+(aq)+S2O42−(aq)→2SO32−(aq)+Cu(s)+4NH3(aq)
The oxidation number of Cu decreases from +2 to 0. Net decrease in the oxidation number is 2.
The oxidation number of S atom increases from +3 to +4. For 2S atoms, the oxidation number increases by 2.
Thus, an increase in the oxidation number is balanced with a decrease in oxidation number.
To balance O atoms, add 2 water molecules on LHS.
Cu(NH3)42+(aq)+S2O42−(aq)+2H2O(l)→2SO32−(aq)+Cu(s)+4NH3(aq)
To balance H atoms, add 4 protons on RHS.
Cu(NH3)42+(aq)+S2O42−(aq)+2H2O(l)→2SO32−(aq)+Cu(s)+4NH3(aq)+4H+(aq)
Since the reaction is in basic medium, add 4 hydroxide ions on either side.
Cu(NH3)42+(aq)+S2O42−(aq)+2H2O(l)+4OH−(aq)→2SO32−(aq)+Cu(s)+4NH3(aq)+4H+(aq)+4OH−(aq)
On RHS, 4 hydrogen ions combine with 4 hydroxide ions to form 4 water molecules out of which 2 water molecules cancel with 2 water molecules on LHS.
Cu(NH3)42+(aq)+S2O42−(aq)+4OH−(aq)→2SO32−(aq)+Cu(s)+4NH3(aq)+2H2O(aq)
This is the balanced chemical equation in basic medium.
The coefficients x,y and z are 4,2 and 4 respectively.