Which of the following species is the least stable?

Which of the following pictorial diagrams most correctly represents the $\pi^*$ ($\pi$-antibonding) molecular orbital between two atoms if the internuclear axis is taken to be in the $z$-direction?

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

Which of the following statements is correct for the peroxide ion $(O_2^{2-})$?
$A.$ It has completely filled $\pi^*$ antibonding molecular orbitals.
$B.$ It is diamagnetic.
$C.$ It has a bond order of one.
$D.$ It is isoelectronic with Neon.

The molecular orbital configuration of a diatomic molecule is
$\sigma 1s^2 \sigma^* 1s^2 \sigma 2s^2 \sigma^* 2s^2 \sigma 2p_x^2 \pi 2p_y^2 \pi 2p_z^2$
Its bond order is

Which of the following molecules would have the same magnetic nature regardless of whether $sp$ mixing is operative or not?