Q. Formation of $He_2$ molecule is not possible because:

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$N _{ b }> N _{ a }$

$N _{ b }< N _{ a }$

$N _{ b }= N _{ a }$

$N _{ b }- N _{ a }$ is -ve

Solution:

No. of electrons in bonding and anti - bonding molecular orbital is same and is equal to $2$
Bond order $= N _{ b }- N _{ a } / 2=2-2 / 2=0$
Therefore no bond exists between $He$ - atom

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