$A$ molecule which contains unpaired electrons is

The total number of species from the following in which one unpaired electron is present,is . . . . . . $N_2, O_2, C_2^{-}, O_2^{-}, O_2^{2-}, H_2^{+}, CN^{-}, He_2^{+}$

How many electrons are present in the antibonding molecular orbitals of the $O_2$ molecule?

The bond order in $O_2^{2-}$ is

$A$ pair of isoelectronic species having bond order of $1$ is

Which one is paramagnetic and has the bond order $1/2$?