The number of unpaired electrons in ""_(27)Co is

Presence of unpaired electrons makes a species paramagnetic. Each unpaired electron has a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is considerably important. For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the spin-only formula, i.e., mu = sqrt(n(n+2)) where n=number of unpaired electrons and mu =magnetic momentin (in Bohr magneton, B.M.). If n=1, then mu = 1.73 B.M . Which one of the following transition metal ions is paramagnetic?

The number of bonding and antibonding electrons in O_2^(2-) ion, respectively are