Correct answer is (d) no reaction
The best I can explain: The compound [Co(NH3)5Cl]SO4 dissociates into a cobalt complex ion and a sulphate ion when dissolved ion water. The sulphate ion does not react with silver ion. On the other hand, the ionisation isomer of [Co(NH3)5Cl]SO4, that is [Co(NH3)5(SO4)]Cl dissociates into cobalt complex ion and Cl ion which reacts with silver ion to precipitate AgCl.