Answer
See answer below.
Work Step by Step
a) $2\ NH_3(aq)+H_2SO_4(aq)\rightarrow (NH_4)_2SO_4(aq)$
b) $CaCO_3(aq)+2\ HCl(aq)\rightarrow CaCl_2(aq)+H_2O(l)+CO_2(g)$
c) $BaCl_2(aq)+2\ AgNO_3(aq)\rightarrow Ba(NO_3)_2(aq)+2\ AgCl(s)$
d) $H_2O(l)+HClO_4(aq)\rightarrow H_3O^+(aq)+ClO_4^-(aq)$