Transition metals form a large number of complexes or coordination compounds in which the metal atoms are bound to a number of anions or neutral molecules. The valence bond theory explain the formation, magnetic behaviour and geometrical shapes while the crystal field theory explains the effect of different crystal fields on the degeneracy of d-orbitals energies of the central metal atom/ion. This provides for the quantitative estimation of orbital separation energies, magnetic moments and spectral and stability parameters.
Two complexes of nickel have same geometry but different magnetic behaviour are:
(A) \(\text{[Ni(CN)}_4]^{2-}\)
(B) \(\text{[Ni(CO)}_4]\)
(C) \(\text{[NiCl}_4]^{2-}\)
(D) \(\text{[Ni(NH}_3)_6]^{2+}\)
Choose the correct answer from the options given below :

1. A (A) and (B) only
2. B (B) and (D) only
3. C (B) and (C) only
4. D (A) and (D) only