The salt used for performing bead test in qualitative inorganic analysis is

Question

(a) $K_2SO_4.Al_2SO_4.24H_2O$
(b) $FeSO_4.(NH_4)_2SO_4.6H_2O$
(c) $FeSO_4.(NH_4)_2(SO_4)_3.6H_2O$
(d) $Na(NH_4)HPO_4.4H_2O$