On addition of ammonium chloride to a solution of ammonium hydroxide,what happens to the concentration of $OH^{-}$ ions?

The commercial salt is purified by passing

Assertion : $Sb_2S_3$ is not soluble in yellow ammonium sulphide. Reason : The common ion effect due to $S^{2-}$ ions reduces the solubility of $Sb_2S_3$.

Pure $NaCl$ is prepared by passing $HCl$ gas through a saturated solution of common salt in water. The principle used is:

$0.01 \ mol$ of a weak acid $HA$ $(K_{a} = 2.0 \times 10^{-6})$ is dissolved in $1.0 \ L$ of $0.1 \ M$ $HCl$ solution. The degree of dissociation of $HA$ is ............. $\times 10^{-5}$ (Round off to the Nearest Integer). [Neglect volume change on adding $HA$. Assume degree of dissociation $<< 1$]

When $H_2S$ gas is passed through a solution containing $HCl$ during qualitative analysis,cations of the second group are precipitated,but cations of the fourth group are not precipitated because: