Question

What will be the order of $I^{st}$ ionisation energy?

• A. Li > Na > K
• B. K > Li > Na
• C. Na > Li > K
• D. Li > K > Na

Answer 1

The correct option is A

Li > Na > K

In a group, the ionisation potential decreases from top to bottom. In the alkali group, the ionisation potential decreases from Li to Cs.

$\underset{eV}{}\underset{5.3}{Li}\underset{5.1}{Na}\underset{4.3}{K}\underset{4.2}{Rb}\underset{3.9}{Cs}$