CBSE Class 12-science Answered

The color of most of the transition metal compounds is due to the presence of incomplete d-sub shell. When anions or ligands approach transition metal ions, their d orbitals do not degenerate. They split into two sets, one consisting of lower energy orbitals (t_2g which includes d_xy, d_yz and d_xz) and the other consisting of higher energy orbitals (e_g which includes d_x2-_y2 and d_z2).This is called crystal field splitting. Thus the electrons can jump from lower energy d-orbitals to higher energy d-orbitals.