Zinc and not copper is used for the recovery of metallic

Zinc and not copper is used for the recovery of metallic

Question
Give reasons for the following :(i) Silver bromide is used in photography. (ii) Most transition metal compounds are coloured.(iii) Zinc and not copper is used for the recovery of metallic silver from complex [Ag(CN)2]-. Explain. (iv) The colour of mercurous chloride, Hg2CI2, changes from white to black when treated with ammonia. (v) The species [CuCI4]2- exists while [CuI4]2- does not (vi) CrO3 is an acid anhydride.