Q. In which of the following arrangements the order is not according to the property indicated against it?
A) $Li < Na < K < Rb$ increasing metallic radius
B) $I < Br < F < Cl$ increasing electron gain enthaly (with negative sign)
C) $B < C < N < O$ increasing first ionisation enthalphy
D) $Al^{3 +} < {Mg}^{2 +} < {Na}^{+} < F^{-}$ increasing ionic size
Explanation
(c)
(a) Metallic radii increase in a group from top to bottom.
Thus, $Li < Na < K < Rb$ is true
(b) Electron gain of enthalpy of $Cl > F$ and decreases along a group.
Thus, $I < Br < F < Cl$ is true.
(c) Ionisation enthalpy increases along a period left to right but due to presence of half-filled orbital in N, ionisation enthalpy of $N > O$.
Thus $B < C < N < O$ is incorrect.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.