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}]

If IUPAC name of an element is "unununium" then correct statement regarding element is:

1. It is a inner transition element

2. It belongs to 8th period in periodic table

3. It is 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

Second electron gain enthalpy :

1. is always negative

2. is always positive

3. can be positive or negative

4. is always zero

Element having highest I.P value is :

1. Ne

2. He

3. Be

4. N

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 :