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

1.	Cl, Br	2.	Ca, Cl
3.	Na, Ca	4.	Na, Cl

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

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

The most non-metallic element among the given elements is

The incorrect order of electronegativity 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. $K^{+}>C{a}^{2+}>C{l}^{-}>S^{2-}$