The ion [co(nh3)6]2+
isoctahedral and high spin. this complex is:
a. paramagnetic, with 1 unpaired electron.
b. paramagnetic, with 3 unpaired electrons.
c. paramagnetic, with 4 unpaired electrons.
d. paramagnetic, with 5 unpaired electrons.
e. diamagnetic.

Explanation:

The answer would be  B.

As paramagnetic with 3 unpaired electrons. Since there are 6 ligands around the Co+2 ion it isoctahedral and these ligands are neutral. This makes the overall charge on the complex +2 and therefore comes from the configuration for Co+2 which is [Ar] 3d7. Since it is in high spin you must fill all the orbitals with at least one electron and then pair up any that remain. If you do this, 3 unpaired electrons remain. Para magnetism occurs in substances with unpaired electrons.