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:

1.	Electron repulsion outweighs the stability gained by achieving noble gas configuration.
2.	O– ion has a comparatively smaller size than the oxygen atom.
3.	Oxygen is more electronegative.
4.	Addition of electrons in oxygen results in a large size of the ion.

Choose the compound which has a maximum bond angle at nitrogen among the following:
1. ${\mathrm{NO}}_2$
2. ${{\mathrm{NO}}_2}^{-}$
3. ${{\mathrm{NO}}_2}^{+}$
4. ${{\mathrm{NO}}_3}^{-}$

Which of the following graph is correct representation between atomic number (Z) and magnetic moment of d-block elements? [Outer electronic configuration : (n-1)d^xns^{1 or 2}]

The correct statement regarding an element with the IUPAC name "unununium" is:

1. It is an inner transition element.

2. It belongs to the 8^th period in the periodic table.

3. It is a transition element.

4. It is a non-transition element.

To which of the following atom, the attachement of electron is most difficult ?

1. Radon

2. Nitrogen

3. Oxygen

4. Radium

Which of the following describes the thermodynamic sign convention for the second electron gain enthalpy?

1. Always negative

2. Always positive

3. Can be positive or negative

4. Always zero

Which of the following elements has the highest I.P. (Ionisation Potential) value?

Which of the following is not a representative element?

1. Tellurium

2. Tantalum

3. Thallium

4. Astatine

The ionization energy boron is less than that of beryllium because :
1. beryllium has a higher nuclear charge than boron
2. beryllium has a lower nuclear charge than boron
3. the outermost electron in boron occupies a 2p-orbital
4. the 2s and 2p-orbitals of boron are degenerate

Select the amphoteric substance in the following :