Element of the third period that is expected to exhibit positive electron gain enthalpy is: 

1.	Na	2.	Al
3.	Cl	4.	Ar

The pair that has both members from the same period of the Periodic Table is 

Isoelectronic pair, among the following, is : 

1. ${\mathrm{ClO}}_2^{-}, {\mathrm{ClF}}_2^{+}$

2. ${\mathrm{IF}}_2^{-}, {\mathrm{I}}_3^{-}$

3. ${\mathrm{Cl}}_2\mathrm{O}, {\mathrm{ICl}}_2^{-}$

4. ${\mathrm{ICl}}_2^{-}, {\mathrm{ClO}}_2$

The incorrect order of electronegativity is :

The most non-metallic element among the given elements is

For the second-period elements, the correct increasing order of first ionisation enthalpy is:

1. Li < Be < B < C < O < N < F < Ne

2. Li < Be < B < C < N < O < F < Ne

3. Li < B < Be < C < O < N < F < Ne

4. Li < B < Be < C < N < O < F < Ne

A configuration with the lowest ionization enthalpy among the following is:
1. \(1 s^2 2 s^2 2 p^5\)$\mathrm{}$\(1 s^2 2 s^2 2 p^5\)
2. \(1 s^2 2 s^2 2 p^3\)
3. \(1 s^2 2 s^2 2 p^6 3 s^1\)
4. \(1 s^2 2 s^2 2 p^6\)

Among the following, the most characteristic oxidation states for lead and tin are, respectively:

1. +4, +2

2. +2, +4

3. +4, +4

4. +2, +2

The correct order of increasing electron affinity for the elements, O, S, F and Cl is:

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

1. $C{a}^{2+}>K^{+}>S^{2-}>C{l}^{-}$

2. $C{l}^{-}>S^{2-}>C{a}^{2+}>K^{+}$

3. $S^{2-}>C{l}^{-}>K^{+}>C{a}^{2+}$

4. $K^{+}>C{a}^{2+}>C{l}^{-}>S^{2-}$