The bond order and magnetic property of acetylide ion are same as that of 

Acetylide ion is ${\mathrm{C}}_2^{2-}$. Total  ${\mathrm{e}}^{-}=6+6+2=14$
$\Rightarrow \mathrm{BO}=3.0$ and diamagnetic.
Out of given options ${\mathrm{NO}}^{+}$ has total 14 electrons 
$\Rightarrow \mathrm{BO}$ of ${\mathrm{NO}}^{+}=3.0$ and it is diamagnetic