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. Fe²⁺, 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-

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⁺

Identify the correct order of the size of the following:

(1) Ca²⁺<K⁺<Ar<S^2-<Cl^-

(2) Ca²⁺<K⁺<Ar<Cl^-<S^2-

(3) Ar<Ca²⁺<K⁺<Cl^-<S^2-

(4) Ca²⁺<Ar<K⁺<Cl^-<S^2-

The electronegativity difference between N and F is greater than that between N and H yet the dipole moment of NH₃ (1.5 D) is larger than that of NF₃ (0.2 D). This is because:

(1) in NH₃ as well as in NF₃ the atomic dipole and bond dipole are in the same direction
(2) in NH₃ the atomic dipole and bond dipole are in the same direction whereas in NF₃ these are in opposite directions
(3) in NH₃ as well as NF₃ the atomic dipole and bond dipole are in opposite directions
(4) in NH₃ the atomic dipole and bond dipole are in the opposite directions whereas in NF₃ these are in the same directions

Magnesium reacts with an element (X) to form an ionic compound. If the ground state electronic configuration of (X) is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^3$, the simplest formula for this compound is: 

1. ${\mathrm{Mg}}_2{\mathrm{X}}_3$

2. ${\mathrm{MgX}}_2$

3. ${\mathrm{Mg}}_2\mathrm{X}$

4. ${\mathrm{Mg}}_3{\mathrm{X}}_2$

The formation of the oxide ion O^2– (g), from the oxygen atom requires first an exothermic and then an endothermic step as shown below, 
$\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^{-};$ ${∆}_{\mathrm{f}}{\mathrm{H}}^0=–141$ $\mathrm{kJ}$ ${\mathrm{mol}}^{-1}$
${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{O}}^{2-}\left(\mathrm{g}\right);$ ${∆}_{\mathrm{f}}{\mathrm{H}}^0=+780$ $\mathrm{kJ}$ ${\mathrm{mol}}^{-1}$

Thus, the process of formation of O^2– in the gas phase is unfavorable even though O^2– is isoelectronic with neon. It is due to the fact that: