The following equation represents which process?M(g) + e– → M–(g)second electron affinitysecond ionisation energyfirst ionisation energyfirst electron affinity

Understanding the Equation

The equation provided, $M(g) + e^- \rightarrow M^-(g)$ describes the process where a neutral atom $M$ in the gaseous state gains an electron $e^-$ to form a negative ion $M^-$.

Analyzing the Options

1. First Ionisation Energy: This refers to the energy required to remove an electron from a neutral atom to form a positive ion. This process is the opposite of what is shown in the equation.

2. Second Ionisation Energy: This is the energy required to remove a second electron from an already positively charged ion. This, again, is not what is represented in the equation.

3. First Electron Affinity: This refers to the energy change that occurs when an electron is added to a neutral atom, resulting in the formation of a negative ion. This matches the process described in the equation.

4. Second Electron Affinity: This is the energy change when a second electron is added to a negatively charged ion. The equation does not represent this process.

Conclusion

Given the analysis, the equation $M(g) + e^- \rightarrow M^-(g)$ represents the process of first electron affinity.