There are 3 unpaired electrons in `[Co(H_(2)O)_(6)]^(2+)` and calculated value of magnetic moment on the basis of `sqrt(n(n+2))` is `3.87 BM`, which is much lower than the experimental value of `4.4 BM`. The reason for this difference is due to :
A. Increase in the number of unpaired electrons during determination
B. Some contribution of orbital angular momentum of electron towards the magnetic moment
C. `d-d^(*)` transition
D. Experimental error