A salt solution on treatment with $H_{2}S{O}_4$(dilute) gives out a gas which turns $K_{2}C{r}_2{O}_7$ paper green and lead acetate paper black. The salt contains

Sulphide gives H₂S gas which turns potassium dichromate paper green and lead acetate paper black.

$N{a}_{2}S+H_{2}S{O}_4\to H_{2}S+N{a}_{2}S{O}_4$

$H_{2}S+Pb{\left(C{H}_{3}COO\right)}_2\to Pbs\downarrow +2C{H}_{3}COOH$

Black ppt

$K_{2}C{r}_2{O}_7+4H_{2}S{O}_4+3H_{2}S\to K_{2}S{O}_4+C{r}_2$$+3S+7H_{2}O$

Green