Among $\mathrm{N}{\mathrm{O}}_2^{+}\mathrm{ },\mathrm{ }{\mathrm{K}\mathrm{O}}_2$ and ${\mathrm{N}\mathrm{a}}_2{\mathrm{O}}_2$ and ${\mathrm{N}\mathrm{a}\mathrm{A}\mathrm{l}\mathrm{O}}_2$ , the paramagnetism exist in-

Decreasing order of stability of ${\mathrm{O}}_2,\mathrm{ }{\mathrm{O}}_2^{-},\mathrm{ }{\mathrm{O}}_2^{+}$ and ${\mathrm{O}}_2^{2-}$ is:

Among the following molecules/ ions, 

${\mathrm{C}}_2^{2-},\mathrm{ }{\mathrm{N}}_2^{2-},{\mathrm{O}}_2^{2-},\mathrm{ }{\mathrm{O}}_2$

Which one is diamagnetic and has the shortest bond length?