Metal gives two chlorides, a and b. Compound a gives a black precipitate with NH₄OH, while compound b gives a white precipitate. Upon reaction with KI, compound b yields a red precipitate soluble in excess of KI. The compounds a and b are respectively:

a) AgCl and ZnCl₂
b) PbCl₂ and AgCl
c) ZnCl₂ and PbCl₂
d) AgCl and PbCl₂