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.

(i) Assertion and reason both are correct statements but reason is not correct explanation

for assertion.

(ii) Assertion is correct statement but reason is wrong statement.

(iii) Assertion and reason both are correct statements and reason is correct explanation

for assertion.

(iv) Assertion and reason both are wrong statements.

Question

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.

(i) Assertion and reason both are correct statements but reason is not correct explanation

for assertion.

(ii) Assertion is correct statement but reason is wrong statement.

(iii) Assertion and reason both are correct statements and reason is correct explanation

for assertion.

(iv) Assertion and reason both are wrong statements.

Philoid · Accepted Answer

(i) Assertion and reason both are correct statements and reason is correct explanation for assertion.

Boron has [He]2s²2p¹ configuration and after donating one electron it attains stable configuration therefore it has smaller first ionisation enthalpy than beryllium which has a completely filled s orbital as it a configuration [He]2s². As 2p electrons are shielded by the inner electrons so it is easy to remove an electron from these orbitals and their ionisation energy decreases.