Q. Ionisation energy in group 1-A varies in the decreasing order as
A) $Li > Na > K > Cs$
B) $Na > Li > K > Cs$
C) $Li > Cs > K > Na$
D) $K > Cs > Na > Li$
Explanation
(a)
Atomic size increases as we move from top to down in a group, therefore, the amount of energy required for ejection of an electron from atom decreases i.e., ionisation energy decreases. Hence, the correct order of $IE_{1}$is
$Li > Na > K > Cs$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.