In which of the following arrangements the order is NOT according to the property indicated against it ?

Options

A. `Al^(3+) lt Mg^(2+) lt Na^(+) lt F^(-)` increasing ionic size
B. BltCltNltO increasing first ionisation energy
C. IltBrltFltCl increasing electron gain enthalpy (without negative charge)
D. Li ltNaltKltRb increasing metallic radius .

Answer

B

Explanation

(A) all of these are isoelectronic ions with decreasing nuclear charge and increasing ionic size
`Al^(3+) (Z=13) lt Mg^(2-) (Z=12) lt Na^(+) (Z=11) lt F^(-) (Z=9)`
(B) `I.E_(1)` of these elements are in the order
BltCltOltN
`I.E_(1)` of N `1s^2s^(2)2p^(3)` is more than `O 1s^(2)2s^(2) 2p^(4)` due to extra stable half filled 2p-subshell in the valence shell. thus, the give order is not correct.
(C) electron gain enthalpies of these elements are
I(-295 k J `mol^(1)`), Cl(-349 k J `mol^(-)`) F(-328 kJ `mol^(-1)`) lt Cl (-349 k J `mol^(-1)`)
(D) Metallic radius increases down the group in 1st group.