The ionisation energy of `A(g)` is similar to in terms of magnitude `-`

Options

A. Electron affinity of A+(g)
B. Electron affinity of A(g)
C. Ionisation energy of A+(g)
D. Ionisation energy of A2+(g)

Explanation

To solve the question regarding the ionization energy of `A(g)` and its similarity in terms of magnitude, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy (IE) is defined as the energy required to remove one electron from an atom in the gaseous state. For atom `A`, this can be represented as:
\[ A(g) \rightarrow A^+(g) + e^- \]
- The energy required for this process is the first ionization energy (IE1).

2. **Understanding Electron Affinity**:
- Electron affinity (EA) is defined as the energy change when an electron is added to a neutral atom in the gaseous state to form a negative ion. For atom `A`, this can be represented as:
\[ A^+(g) + e^- \rightarrow A(g) \]
- The energy released in this process is the first electron affinity (EA1).

3. **Relating Ionization Energy and Electron Affinity**:
- It is important to note that the magnitudes of ionization energy and electron affinity are related but have opposite signs. Specifically:
\[ IE = -EA \]
- This means that while ionization energy is the energy required (positive value), electron affinity is the energy released (negative value). However, in terms of magnitude, they are equal:
\[ |IE| = |EA| \]

4. **Conclusion**:
- Therefore, we can conclude that the ionization energy of `A(g)` is similar in magnitude to the electron affinity of `A^+(g)`. Thus, the answer to the question is that the ionization energy of `A(g)` is equal in magnitude to the electron affinity of `A^+(g)`.

### Final Answer:
The ionization energy of `A(g)` is similar in magnitude to the electron affinity of `A^+(g)`.