The correct order for electron affinity of halogens is :

1. Br > F

2. F > Cl

3. Br > Cl

4. F > I

Values of electronegativity like 3.0, 2.8, 2.5 are related to :-

(1) Elements having low IP in the periodic table

(2) Elements having high EA in the periodic table

(3) Chalcogens

(4) None of the above

The pair of elements where the addition of a second electron to each atom is endothermic is:

1. N, Ne

2. Be, F

3. B, C

4. All of the above

The incorrect match among the following is:

1. B < C < N < O (increasing first ionisation enthalpy)

2. I < Br < F < Cl (increasing electron gain enthalpy)

3. Li < Na < K < Rb (increasing metallic radius)

4. Al³⁺ < Mg²⁺ < Na⁺ <F^- (increasing ionic size)

The formation of the oxide ion O^2-(g), from oxygen atom requires first an exothermic and

then an endothermic step as shown below,

$\mathrm{O}\left(\mathrm{g}\right) + \mathrm{e}- \stackrel{ }{\to } {\mathrm{O}}^{-}\left(\mathrm{g}\right); {∆}_{\mathrm{f}}\mathrm{H}° = -141{\mathrm{kJmol}}^{-1}$
${\mathrm{O}}^{-}\left(\mathrm{g}\right) +\hspace{0.17em}{\mathrm{e}}^{-} \stackrel{ }{\to }{\mathrm{O}}^{2-}\left(\mathrm{g}\right); {∆}_{\mathrm{f}}\mathrm{H}° = +780 \mathrm{kJ} {\mathrm{mol}}^{-1}$

Thus, process of formation of O^2- in gas phase is unfavourable even though O^2- is

isoelectronic with neon. It is due to the fact that

1. electron repulsion outweighs the stability gained by achieving noble gas configuration

2. O^- ion has comparatively smaller size than oxygen atom

3. Oxygen is more electronegative

4. addition of electron in oxygen result in large size of the ion