The correct option is A 2Na[Ag(CN)2]+Zn→Na2[Zn(CN)4]+2Ag
In option (b),
only the oxidation state of Ba increases i.e it is oxidised but no other element is reduced
In option (c), Oxidation state of no element changes and the same thing happens in option (d)
In option (a),
oxidation state of Ag reduces from +1 to 0 hence it is oxidised and the oxidation state Zn increases from 0 to +2 hence it is reduced
So, its a redox reaction