# In which species would 2 unpaired electrons be present in the ground state: "a. sodium atom;" "b. cobalt atom;" "c. iron dication," Fe^(2+); "d. iron atom?"

$\text{Option (d)}$.
We can immediately eliminate $N a$, $Z = 11$, and $C o$, $Z = 27$, because these give rise to an odd number of electrons in the ground state, the which must necessarily be UNPAIRED.
As regards, $b .$, i.e. $F e$, we have $Z = 26$, however, Hunds' rule dictates a configuration of $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2} 3 {d}^{6}$. In the isolated ATOM, we must fit 6 electrons into the 5 valence $\text{d-orbitals}$. At least 2 of the electrons must be unpaired.