In the analysis of $III$ group basic radicals of salts,the purpose of adding $NH_4Cl_{(s)}$ to $NH_4OH$ is

• A
  to increase the concentration of $OH^{-}$ ions
• B
  to precipitate the radicals of group $IV$ and $V$
• C
  to suppress the dissociation of $NH_4OH$
• D
  to introduce $Cl^{-}$ ions