Which statements are correct for the peroxide ion?

$N_2$ and $O_2$ are converted to monocations $N_2^+$ and $O_2^+$ respectively. Which statement is wrong?

Two $\pi$ and half $\sigma$ bonds are present in

The sum of bond order of $O_2^{+}$,$O_2^{-}$,$O_2$ and $O_2^{2+}$ is equal to

Consider the following statements.
$I$. In the conversion of $O_2$ to $O_2^{2+}$,bond order decreases.
$II$. In the conversion of $O_2$ to $O_2^{2+}$,magnetic property is not changed.
$III$. In the conversion of $O_2$ to $O_2^{2+}$,bond length decreases.
$IV$. $O_2^{2-}$ and $B_2$ have same bond order.
Identify the correct statements.

Arrange the molecules $B_2, He_2, N_2$ and $C_2$ in the increasing order of their bond order values.