An element has electronic configuration as $1s^2,2s^2$ $2p^6,3s^{2}3p^6,4s^2,3d^7$.

The correct statement regarding element is :

The electronic configuration of cobalt (Co) is $1s^2, 2s^2$, $2p^6,3s^{2}3p^6,4s^2,3d^7$. Cobalt lies in the group 9, The maximum number of electron is 6. Cobalt has 3 unpaired electrons. The magnetic moment of the compound is,

$\mu =n(n+2)$

$\mu =3(3+2)$

 $\mu =15BM$

Hence, all the statement about the cobalt is correct.