Question

The process requiring the absorption of energy is

• A. $\mathrm{F}\to {\mathrm{F}}^{–}$
• B. $\mathrm{Cl}\to {\mathrm{Cl}}^{–}$
• C. ${\mathrm{O}}^{-}\to {\mathrm{O}}^{2-}$
• D. $\mathrm{H}\to {\mathrm{H}}^{-}$

Answer 1

The correct option is C

${\mathrm{O}}^{-}\to {\mathrm{O}}^{2-}$

Explanation for correct option:

(C) ${\mathrm{O}}^{-}\to {\mathrm{O}}^{2-}$

• When one electron is added to oxygen $\mathrm{O}:1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^4$ it becomes ${\mathrm{O}}^{-}:1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^5$ .
• When another electron is added to oxygen $\left({\mathrm{O}}^{2-}:1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^6\right)$ , the electron that is already present repels the incoming electron.
• Hence, it needs more absorption energy to add an electron.

Explanation for incorrect option:

(A) $\mathrm{F}\to {\mathrm{F}}^{–}$

• The fluorine requires one electron to attain noble gas configuration so it does not require absorption energy to add it. So, it is an incorrect option.

(B) $\mathrm{Cl}\to {\mathrm{Cl}}^{–}$

• The chlorine requires one electron to attain noble gas configuration so it does not require absorption energy to add it. So, it is an incorrect option.

(D) $\mathrm{H}\to {\mathrm{H}}^{-}$

• It is easier to add an electron to hydrogen in $\mathrm{p}-$orbital, so it does not require absorption energy to add an electron. So, it is an incorrect option.

Hence, the correct option is (C) ${\mathrm{O}}^{-}\to {\mathrm{O}}^{2-}$.