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4.Chemical Bonding and Molecular Structure
medium
In which of the following pairs of molecules/ions, both the species are not likely to exist?
A
$H_{2}^+, He_2^{2-}$
B
$H_{2}^-, He_2^{2-}$
C
$H_{2}^{+2}, He_2$
D
$H_{2}^-, He_2^{2+}$
(JEE MAIN-2013)
Solution
Species having zero or negative bond order do not exist.
$\mathrm{H}_{2}^{2+}(1+1-2=0)=\sigma 1 \mathrm{s}^{0}$
Bond order $=0$
$\mathrm{He}_{2}(2+2=4)=\sigma 1 \mathrm{s}^{2},{ }^{\star} \mathrm{fs}^{2}$
Bond order $=\frac{N_{0}-N_{a}}{2}=\frac{2-2}{2}=0$
$\mathrm{So}, \mathrm{both} \mathrm{H}_{2}^{2+}$ and $\mathrm{He}_{2}$ do not exist.
Standard 11
Chemistry
