Q. The order of first ionisation energies of the element Li, Be, B, Na is
A) $Li > Be > B > Na$
B) $Be > B > Li > Na$
C) $Na > Li > B > Be$
D) $Be > Li > B > Na$
Explanation
(b)
Ionisation energies increase in a period on moving left to right while it decreases in a group on moving downward. The IE of Be is greater than B due to completely filled $s$-orbital. Hence, the order of IE is as
$Be > B > Li > Na$.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.