Question

H2 molecule exist but he2 molecule does not
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Answer 1

is 2 molecule is exist because the hydrogen has a complete electronic configuration, but the idiom is a noble gas, and also I am not gas, so has it held up Philip electronic configuration and it does not combine with helium to form a diatomic molecule

Answer 2

h2 molecule exists because it has two filled orbitals so it combines with two half filled orbital to complete its octet. that why H2 is formed.

he2 cannot be formed because as it has fully filled atomic orbital so it does not combine with another atomic orbital .so He2 is not formed