Question

Why zn2+ salts are white while ni2+ salts are coloured. ?

Answer 1

Explanation:

Generally most d-block elements produce coloured salts since the aqueous ions of many transition elements can absorb energy released during the  reaction and can get excited and emit that energy in the form of radiation in the visible light region of the electromagnetic spectrum when returning to the ground state producing various colours due to the presence of partially filled d subshells. But in the case of Zn which also belongs to d block does not produce coloured salts due to absence of partially filled d subshells when they produce Zn²⁺ ion which is the only stable ion produced by Zn. (Due to absence of partially filled d subshells Zn is known as a non-transition element.)

Electronic configuration of Zn²⁺ → 1s²2s²2p⁶3s²3p⁶3d¹⁰4s⁰

But for Ni²⁺, it does have partially filled d subshells thus they produce coloured salts.

Electronic configuration of Ni²⁺ → 1s²2s²2p⁶3s²3p⁶3d⁸4s⁰