In each of the following sets of elements which element woul

In each of the following sets of elements, which element would be expected to have the highest ionization energy?

a. Cs, K, Li

b. Ba, Sr, Ca

c. I, Br, Cl

d. Mg, Si, S

Solution

Ionization energy is the amount of energy required to remove a single electron from the outer most shell of an atom.
General trend is
The ionization energy decreases from top to bottom in groups, and increases from left to right across a period.(effective nuclear charge increases.)
(i) In first case all elements are placed in the same group, therefore ionization energy will decrease on moving from top to down the group, so correct order is
Li > K > Cs
(ii) Here all elements are placed in the same group, therefore ionization energy will decrease on moving from top to down the group, so correct order is
Ca > Sr > Ba
(iii) similar trend therefore order
Cl > Br > I
(iv) Here in this case we move across the the group and we know that when we move across the group from left to right ionization energy increases.Hence correct order is
S > Si > Mg