Classification of Elements and Periodicity in Properties · Question 26

Given below are two statements : In the light of the above statements, choose the most appropriate answer from the options given below :

1. Statement I is incorrect but Statement II is correct
2. Both Statement I and Statement II are correct
3. Statement I is correct but Statement II is incorrect
4. Both Statement I and Statement II are incorrect

Answer

(2) Both Statement I and Statement II are correct

Solution

Statement I: Mg2+, Na+, F- and O2- are isoelectronic (10 electrons each).

For the same number of electrons, radius decreases as nuclear charge increases.

Nuclear charge: Mg (12) > Na (11) > F (9) > O (8)

Radius: Mg2+ < Na+ < F- < O2- Statement I is correct.

Statement II: Electron gain enthalpies ( kJ mol-1): Cl = -349, F = -328, Br = -325, I = -295.

F is very small, the added electron suffers strong repulsion from the compact 2p electrons, so F releases less energy than Cl.

Magnitude: Cl > F > Br > I Statement II is correct.

Answer: (2)