In which of the following pairs of molecules / ions , both the species are not likely to exist ?

Question

$\begin{array}{1 1} (1) H_2^+,He^{2-}_2 \\ (2) H_2^-,He^{2-}_2 \\ (3) H_2^{2+},He_{2} \\ (4) H_2^{-},He^{2+}_{2} \end {array}$