According to molecular orbital theory,the species among the following that does not exist is

Bond order of $O_2$ is

$He_{2}$ molecule is not possible. Explain.

$A$ molecule which contains unpaired electrons is

The internuclear distances in $O-O$ bonds for $O_2^+$,$O_2$,$O_2^-$ and $O_2^{2-}$ respectively are

If $x-axis$ is the molecular axis and $p_z$ orbitals participate in bonding,then which one of the following will be the nodal plane present within the $\pi-$ bond of the $O_2$ molecule?