Question

Which one of K, I, Cl and Li Will display the highest first ionisation energy ?

• A. K
• B. I
• C. Cl
• D. Li

Answer 1

Answer: (C)

Cl

The ionisation energy increases on moving from left to right along a period, because with increase in atomic number in a period, effective nuclear charge increases and so, electrons are more tightly held. Whereas, on moving down a group, the valence shell becomes far away from the nucleus and thus, nuclear attraction towards valence electron decreases which results in decrease in ionisation energy. Thus, chlorine has the highest first ionisation energy among all the given elements.