question_answer 97)

  Assertion (A): Boron has a small first ionisation enthalpy than beryllium. Reason (R): The penetration of a 2s-electron to the nucleus is more than 2p-electron, hence 2p 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. (c) Assertion and Reason both are correct statements and Reason is correct explanation for Assertion. (d) Assertion and Reason both are wrong statements.

Answer:

  (c) Boron (\[1{{s}^{2}},2{{s}^{2}}2{{p}^{1}}\]) has less first ionisation enthalpy than beryllium (\[1{{s}^{2}},2{{s}^{2}}\]) because beryllium has fully filled s-subshell. 2s-electrons are nearer to the nucleus as compared to 2p-electrons.