For the percipitation of cations of group four in the qualitative analysis, the medium is made alkaline before passing $H_2S$ gas. The purpose of alkaline Solution is

Question

(a) to supress the ionisation of $H_2S$

(b) to increase the ionisation of $H_2S$

(c) to increase the ionisation of metal salt

(d) to decrease the ionisation of metal salt.