The bond order and magnetic behaviour of $O_2$ molecule are respectively. 

Total no. of electrons in $O_2$ molecule = 16.

$\sigma 1s^2\sigma *1s^2\sigma 2s^2\sigma *2s^2\sigma 2{p_z}^2\pi 2p{x}^2=\pi 2{p_y}^2\pi *2p{x}^1=\pi *2p{y}^1$

Bond order $=\frac{\left(No.ofbondingelectrons-No.ofantibondingelectrons\right)}{2}$$=\frac{(10-6)}{2}=\frac{4}{2}=2$

Due to presence of unpaired electron in antibonding molecular orbital it is paramagnetic.