Element which has the lowest ionisation potential among the following is:

1.	C	2.	Si
3.	Sn	4.	Pb

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

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

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: