Right choice is (a) 1:1
The explanation: Werner observed that ‘x’ mol of AgCl was precipitated per mole of CoCl3.4NH3 with excess silver nitrate. Currently, there are seven groups attached to the cobalt atom. For the secondary valence to be six, one of the chloride (x=1) has to be precipitated as AgCl, therefore 1:1 electrolyte.