Question

Which of the following is the correct order of ionisation energy?
(1) `Be^(+) gt Be` (2) `Be gt Be^(+)`
(3) `C gt Be` (4) `B gt Be`
A. 2,3
B. 3,4
C. 1,3
D. 1,4

Answer 1

Correct Answer - C
(1) `Be` has completely filled stable valence shell configuration i.e. `2s^(2)` while in `Be^(+)` because of positive charge, the removal of electron requires much higher energy. So, ionisation energy of `Be^(+)` is greater than `Be`
(3) Across the period, atomic size decreases and nuclear charge increases and thus valence shell electron(s) is//are tightly held by nucleus. So, ionisation energy of `C` is greater than `Be`.