An example of metalloid elements in the periodic table is:

1.	Na and K	2.	Cu and Al
3.	As and Si	4.	Ca and Mg

Sodium generally does not show an oxidation state of +2, because of:

1. High first ionization potential.

2. High second ionization potential.

3. Large ionic radius.

4. High electronegativity.

Element that has the greatest tendency to lose an electron is :

Amongst the following electronic configurations, the highest ionization energy
is represented by:

1. [Ne]3s²3p³

2. [Ne]3s²3p²

3. [Ar]3d¹⁰4s²4p³

4. [Ne]3s²3p¹

The electronic configuration that represents the d-block element is: 

1. 1s² 2s² 2p⁶ 3s²3p⁶3d¹⁰ 4s²4p⁶

2. 1s² 2s² 2p⁶ 3s²3p⁶3d¹⁰ 4s²4p¹

3. 1s² 2s² 2p⁶ 3s²3p⁶3d¹⁰ 4s²

4. 1s² 2s² $2p^6$ 3s²3p⁶ 4s²

Which of the following exhibits variable oxidation states?

Among the following species, the smallest ion is : 

Allred Rochow's scale is related to:
 

1. Electronegativity, radius, and Z^*

2. Resonance energy of the molecule, ionisation potential and electron affinity.

3. Bond Polarity, diagonal relationship and periodicity.

4. None of the above.

The incorrect match among the following is:

1. B < C < N < O (increasing first ionisation enthalpy)

2. I < Br < F < Cl (increasing electron gain enthalpy)

3. Li < Na < K < Rb (increasing metallic radius)

4. Al³⁺ < Mg²⁺ < Na⁺ <F^- (increasing ionic size)

The correct order of increasing electron gain enthalpy with a negative sign for the elements O, S, F, and Cl is : 

1. Cl < F < S < O                   

2. O < S < F < Cl

3. F < S < O < Cl                   

4. S < O < Cl < F