Which of the following substances is paramagnetic ?

${\mathrm{Na}}_2{\mathrm{O}}_2:$${\mathrm{Na}}^{+}$ has all electrons paired and ${\mathrm{O}}_2^{-2}$ has no unpaired electron 

${\mathrm{N}}_2\mathrm{O}\text{ : }$all electrons are paired so it is diamagnetic

 ${\mathrm{KO}}_2\text{ : }$ ${\mathrm{K}}^{+}$ has all electrons paired and ${\mathrm{O}}_2^{-}$ has one unpaired electron so it is paramagnetic

Hence the correct answer is (C) ${\mathrm{KO}}_2$