MCQ
Note : In the following questions a statement of Assertion $(A)$ followed by a statement of reason $(R)$ is given. Choose the correct option out of the choices given below each question.
Assertion $(A)$ : Boron has a smaller first ionisation enthalpy than beryllium.
Reason $(R)$ : The penetration of a $2s$ electron to the nucleus is more than the $2p$ electron hence $2p$ electron is more shielded by the inner core of electrons than the $2s$ electrons.
  • A
    Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  • B
    Assertion is correct statement but reason is wrong statement.
  • Assertion and reason both are correct statements and reason is correct explanation for assertion.
  • D
    Assertion and reason both are wrong statements.

Answer

Correct option: C.
Assertion and reason both are correct statements and reason is correct explanation for assertion.
Boron $\left(1 s^2 2 s^2 2 p^1\right)$ has less first ionisation enthalpy than beryllium $\left(1 s^2 2 s^2\right)$ because beryllium has fully filled. $s-$ sub shell. $2 s -$ electrons are nearer to the nucleus as compared to $2 s -$ electrons.

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