Which of the following pairs of elements would you expect to have lower first ionisation energy?
a.`Cl` or `F`
b.`Cl` or `S`
c.`K` or `Ar`
d.`Kr` or `Xe`

Answer

(i) CI (ii) S (iii) K (iv) Xe

Explanation

(i) Because of the bigger size the stronger shielding effect CI has lower `Delta_(i) H_(1)` than F .
(ii) Among s and CI S has lower `Delta_(i) H_(1)` due to bigger size and lower nuclear charge
(iii) K has lower `Delta_(i) H_(1)` than Ar has configuration .
(iv) Xe because of its bigger size and stronger shielding effect has lower `Delta_(i) H_(1)` than Kr.