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JEE Main levelSingle correct optionDifficulty 2 of 3pt013

Which element has its valence electrons only in an $n s^{2}$ configuration, yet is placed in group 18?

AHe
BBe
CNe
DMg

Answer: A

Helium is

1 s^{2}

and has a completely filled first shell, so it is placed with the noble gases in group 18. Be and Mg are

n s^{2}

elements of group 2, and Ne is

2 s^{2} 2 p^{6}

.

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