Q. Generally, the first ionisation energy increases along a period. But there are some exceptions. One which is not an exception is
A) N and O
B) Na and Mg
C) Mg and Al
D) Be and B
Explanation
(b)
Na belongs to IA group and Mg belongs to IIA group. On moving from left to right in a period, first ionisation energy increases, thus, IE of Mg is greater than the IE of Na.
IE order
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Mg > Na$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.