# Three separate samples of a solution of a single salt gave these results. One formed a white ppt. with excess ammonia solution, one formed a white ppt. with dil. NaCl solution and one formed a black ppt. with $H_2S$. The salt could be:

(a) $AgNO_3$
(b) $Pb(NO_3)$
(c) $Hg(NO_3)_2$
(d) $MnSO_4$

Answer: $Pb(NO_3)_2$

$Pb(NO_3)_2 + 2NH_4OH \longrightarrow Pb(OH)_2 \downarrow (\text{white ppt.}) + 2NH_4NO_3$
$Pb(NO_3)_2 + 2NaCl \longrightarrow PbCl_2 \downarrow (\text{white ppt.}) + 2NaNO_3$
$Pb(NO_3)_2 + H_2S \longrightarrow PbS \downarrow (\text{black ppt.}) + 2NaNO_3$