$$ \ text {pb(no} _3 \ text {)} _ 2 \ text {(aq) + 2nh} _3 \ text {(aq)} \ rightleftharpoons $ $ $ \ text {[pb(nh}} _3 \ \ text {)} _ 2]² + _ { \ text {2no} _3^-_ {(aq)} $$
$$ \ text {pb(no} _3 \ text {)} _ 2 \ text {(aq) + 2nh} _3 \ text {(aq)} \ rightleftharpoons $ $ $ \ text {[pb(nh}} _3 \ \ text {)} _ 2]² + _ { \ text {2no} _3^-_ {(aq)} $$