electron configuration in coordination complexes

[Nimisha_Seshadri_3C]

2) In which of the following species does the transition metal ion have d3
electronic configuration?
a. [Co(OH2)6]2+
b. [Cr(NH3)6]3+
c. [CoF6]3-
d. [Fe(CN)6]3-
e. [Ni(OH2)6]2+

[Sristi Palimar 2E]

The answer would be [Cr(NH3)6]3+.

The question asks for species does the transition metal ion have d^3. In other words, which species does the transition metal contains d^3 in part of its electron configuration. (NH3)6 has a neutral charge, therefore Cr must carry the 3+ charge. The electron configuration for Cr3+ is [As]3d^3.