Correct decreasing order of bond order of oxygen species in $I$ to $IV$

$(I)$   $Na_2O_2$

$(II)$  $O_2 [AsF_6]$

$(III)$  $CsO_2$

$(IV)$  $O_2$

When two atomic orbitals combine they form

Among the following, the molecule expected to be stabilized by anion formation is

Number of molecules/species from the following having one unparred electron $15$. . . . . .  $\mathrm{O}_2, \mathrm{O}_2^{-1}, \mathrm{NO}, \mathrm{CN}^{-1}, \mathrm{O}_2^{2-}$

What is meant by the term bond order ? Calculate the bond order of: $N _{2}, O _{2}, $ $O _{2}^{+}$ and $O _{2}^{-}$

Atomic number of an element is $26.$ The element shows