#[Mo(OH_2)_6]^(3+)# is a paramagnet due to the electronic configuration of the metal ion.
Explanation:
The #Mo^(3+)# is a #d^3# ion. Coordination chemistry would predict that the #d# electrons were all unpaired, and therefore give rise to paramagnetism. Even if only 1 of the electrons were unpaired (which is a necessity!) the complex would still be a paramagnet).