The correct sequence of increasing radii is - 

1.	Ar < K+ < Ca2+	2.	Ca2+ < Ar < K+
3.	Ca2+ < K+ < Ar	4.	K+ < Ar < Ca2+

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

Which of the following orders of ionic radii is correctly represented?

1. H^->H>$H^{+}$

2. Na⁺>F^->O^2-

3. F^->O^2->Na⁺

4. N^3->Mg²⁺<Al³⁺

Be²⁺ is isoelectronic with which of the following ions?

1. H⁺

2. Li⁺

3. Na⁺

4. Mg²⁺

A pair among the following that have the same size is:

1. Fe³⁺, Ni²⁺

2. Zr⁴⁺, Ti⁴⁺

3. Zr⁴⁺ , Hf⁴⁺

4. Zn²⁺, Hf⁴⁺

The correct order of the decreasing ionic radii among the following isoelectronic species is : 

1. Ca²⁺ > K⁺ > S^2- > Cl^-

2. Cl^- > S^2- > Ca²⁺ > K⁺

3. S^2- > Cl^- > K⁺ > Ca²⁺

4. K⁺ > Ca²⁺ > Cl^- > S^2-

The correct order of increasing electron gain enthalpy with a negative sign for the elements O, S, F, and Cl is : 

1. Cl < F < S < O                   

2. O < S < F < Cl

3. F < S < O < Cl                   

4. S < O < Cl < F

Which one of the following compounds is a peroxide ?

1. KO₂

2. BaO₂

3. MnO₂

4. NO₂

The sequence of ionic mobility in aqueous solution is

1. K⁺>Na⁺>Rb⁺>Cs⁺

2. Cs⁺>Rb⁺>K⁺>Na⁺

3. Rb⁺>K⁺>Cs⁺>Na⁺

4. Na⁺>K⁺>Rb⁺>Cs⁺

Which one of the following arrangements does not give the correct picture of the trends indicated against it?

(1) F₂ > Cl₂ > Br₂ > I₂ :Oxidising power

(2) F₂ < Cl₂ > Br₂ > I₂ : Electron gain enthalpy

(3) F₂ > Cl₂ > Br₂ > I₂ : Bond dissociation energy

(4) F₂ > Cl₂ > Br₂ > I₂: Electronegativity