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Question

# Assertion : Two electrons of helium atom are placed in only one shell but three electrons of lithium need two shells. Reason: A shell can have maximum 2n2 electrons.

A
Assertion is correct but the reason is incorrect
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B
Assertion is incorrect but the reason is correct
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C
Both assertion and reason are correct but reason is not the correct explanation for the assertion
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D
Both assertion and reason are correct and the reason is the correct explanation for the assertion
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Solution

## The correct option is D Both assertion and reason are correct and the reason is the correct explanation for the assertionA shell can have maximum 2n2 electrons. Here, K-shell is the 1st shell and L-shell is the 2nd shell. That is; For K-shell, n=1, 2 x 12=2 And for L-shell, n=2, 2 x 22=8 K-shell and L-shell can have maximum 2 and 8 electrons respectively. Helium atom has 2 electrons and both these electrons are placed in the K-shell. Lithium atom has 3 electrons; 2 in K-shell and 1 in L-shell. Thus, the reason is the correct explanation for the assertion.

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