Which of the following pairs has the most significant size variation?

1.	Na and Na+	2.	Na and K
3.	Cl and Cl–	4.	Mg and Mg+

Which is the correct order of ionization energies?

Which of the following options shows an incorrect order of ionic radii?

1. Sr²⁺<Rb⁺<Br^-<Se^2-

2. Nb⁵⁺<Zr⁴⁺<Y³⁺

3. Co>Co²⁺>Co³⁺>Co⁴⁺

4. Ba²⁺>Cs⁺<Se^2-<As^3-

The element having electronic configuration [Kr]4d¹⁰4f¹⁴, 5s²5p⁶, 6s² belongs to:

1. s-block

2. p-block

3. d-block

4. f-block

The atomic species that has the maximum ionization energy is : 

In the II period, the most acidic oxide is formed by:

1. F

2. N

3. O

4. Li

The correct order of ionization energies for the elements Si, P, Ge, and As, from lowest to highest, is:

1st (∆H₁) and 2nd  (∆H₂) Ionization Enthalpies (in kJ mol^–1) and the (∆_egH) Electron Gain Enthalpy (in kJ mol^–1) of a few elements are given below:

The most reactive metal is:

The process that is not endothermic in nature, is : 

1. $A{r}_{\left(g\right)}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>e^{-}<mspace\; width="1em"></mspace>\to <mspace\; width="1em"></mspace>A{r}_{\left(g\right)}^{-}$

2. $N{a}_{\left(g\right)<mspace\; width="1em"></mspace>}\to <mspace\; width="1em"></mspace>N{a}_{\left(g\right)}^{+}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>e^{-}$

3. $H_{\left(g\right)}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>e^{-}<mspace\; width="1em"></mspace>\to <mspace\; width="1em"></mspace>H_{\left(g\right)}^{-}$

4. $O_{\left(g\right)}^{-}<mspace\; width="1em"></mspace>+<mspace\; width="1em"></mspace>e^{-}<mspace\; width="1em"></mspace>\to <mspace\; width="1em"></mspace>O_{\left(g\right)}^{2-}$

Given below are pair of species. Which pair has the largest difference in sizes?