Question

The first ionisation energy is maximum for:

• A. $Rb$
• B. $K$
• C. $Na$
• D. $Kr$

Answer 1

The correct option is D $Kr$

$Na,K$ and $Rb$ are alkali metals and have low ionisation energies. $Kr$ on the other hand is a noble gas and has a high ionisation energy owing to its fully filled outer orbital.