Predict which of the following transition metal ions has a color cr3+, cd2+, hg2+, v2+

Cr3+ is green and V2+ is purple. Cr3+ and V2+ are both d3 so there can be a lot of movement between energy levels to produce colored light. Cd2+ and Hg2+ are both d10 (full d orbital, much less electron movement).

Explanation:

Cr3+ and V2+

Explanation:

Cd and Hg belong to group 12 which is sometimes referred to as post transition elements. They possess a filled d subshell (d10). Remember that the colour of transition elements is attributed to the presence of partially filled d orbitals leading to transition between the three degenerate lower energy t2g orbitals and two higher energy degenerate eg orbitals. If the element has a d10 configuration, such transition is impossible, hence its ions will be colourless.