d
In one case, on electrolysis of aqueous solution, the complex ion of cobalt i.e., \([Co(NH_3)_6]^{3+}\) of the complex \([Co(NH_3)_6][Cr(NO_2)_6]\)  moves towards cathode (i.e., negative electrode) and on this electrode finally cobalt would be deposited. In another case, on electrolysis of aqueous solution, the complex ion of chromium i.e., \([Cr(NH_3)_6]^{3+}\) of the complex \([Cr(NH_3)_6][Co(NO_2)_6]\) moves towards cathode (i.e., negative electrode) and on this electrode chromium would finally be deposited.