Question

Which of the following is the energy-releasing process?
(A) ${X^ - }\xrightarrow{{}}X(g) + {e^ - }$
(B) ${O^ - }(g) + {e^ - }\xrightarrow{{}}{O^{2 - }}$
(C) ${O^ - }(g)\xrightarrow{{}}O(g) + {e^ - }$
(D) ${O^{}}(g) + {e^ - }\xrightarrow{{}}{O^ - }(g)$

Answer 1

Hint: In this question, we should know the basic knowledge of chemical reactions, ionization enthalpies, electron gain enthalpies, and energy released or absorbed in the reaction. Consider these basic terms to find the energy-releasing process.

Complete step by step solution
Let’s understand the terms ionization enthalpy and electron gain enthalpy. It is the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule.
Electron gain enthalpy is the energy required to add an electron to a neutral atom.
Option (A) ${X^ - }\xrightarrow{{}}X(g) + {e^ - }$ represents ionization enthalpy. As in this reaction, one electron is removed. So, energy is required to remove an electron from a neutral gaseous atom.
Option (B) ${O^ - }(g) + {e^ - }\xrightarrow{{}}{O^{2 - }}$ represents the second electron gain enthalpy as the second electron is added to the gaseous molecule. The second electron gain enthalpy is $ + 780KJ/mol$. Which is positive means the energy required to add a second electron to the gaseous atom.
Option (C) ${O^ - }(g)\xrightarrow{{}}O(g) + {e^ - }$ this process is the same as option (A). This process also represents the ionization enthalpy. In this process, an electron is removed from a gaseous atom or molecule. So, here some amount of energy is required to remove an electron from a neutral gaseous atom.
Option (D) ${O^{}}(g) + {e^ - }\xrightarrow{{}}{O^ - }(g)$ represents the first electron gain enthalpy of oxygen. The electron gain enthalpy is $ - 141KJ/mol$. The electron gain enthalpy is negative which means energy is released when an electron is added to a neutral gaseous atom or molecule.
This is the only energy-releasing process.
Therefore, the correct option is (D).

Note:
It is to be noted that when the value of energy is negative the energy is released during the process. When the value of energy is positive energy is absorbed or required during the process.