The second-period element, for example, $\mathrm{F}$ has less electron gain enthalpy than the third-period element of the same group for example $\mathrm{Cl}$. Why?

In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical?

(A) $\mathrm{Rb}$ and $\mathrm{Cs}$

(B) $\mathrm{Na}$ and $\mathrm{K}$

(C) $\mathrm{Ar}$ and $\mathrm{Kr}$

(D) $\mathrm{I}$ and $\mathrm{At}$

Choose the correct answer from the options given below:

What is the correct oder of electron gain enthalpy of $\mathrm{Cl}, \mathrm{F}, \mathrm{Te}, \mathrm{Po}$

The difference between electron gain enthalpies will be maximum between :

Which of the following reactions does not involve absorption of energy?

I. $\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{O}}^{-}\left(\mathrm{g}\right)$

II. $\mathrm{S}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{S}}^{-}\left(\mathrm{g}\right)$

III. ${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{O}}^{2-}\left(\mathrm{g}\right)$

IV. $\mathrm{Cl}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{Cl}}^{-}\left(\mathrm{g}\right)$

Arrange the following according to the instruction given in bracket:

$\mathrm{F}, \mathrm{B}, \mathrm{N}, \mathrm{O}$ (In the increasing order of electron affinity)