The ion that has ${\mathrm{s}\mathrm{p}}^3{\mathrm{d}}^2$ hybridization for the central atom 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?