Assertion: Helium has the highest value of ionisation energy among all known elements.
Reason: Helium has the highest value of elelctron affinity among all known elements.

Options

A. If both assertion and reason are true annd the reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but the reason is false
D. if assertion is false but the reason is true

Answer

To solve the question, we need to evaluate both the assertion and the reason provided.

### Step 1: Evaluate the Assertion
The assertion states that "Helium has the highest value of ionisation energy among all known elements."

- **Explanation**: Ionization energy is the energy required to remove an electron from an atom in its gaseous state. Helium, with the electronic configuration of 1s², has a very strong effective nuclear charge acting on its electrons. This strong attraction makes it difficult to remove an electron, resulting in a high ionization energy. In fact, helium does have the highest ionization energy of all elements.

- **Conclusion**: The assertion is **True**.

### Step 2: Evaluate the Reason
The reason states that "Helium has the highest value of electron affinity among all known elements."

- **Explanation**: Electron affinity is the energy change that occurs when an electron is added to a neutral atom in the gaseous state. For helium, which already has a full outer shell (1s²), adding an electron would require energy rather than releasing it, as it would lead to an unstable configuration (1s² → 1s²1p¹). Thus, helium does not have a high electron affinity; in fact, it has a very low or even negative electron affinity.

- **Conclusion**: The reason is **False**.

### Final Evaluation
- The assertion is **True**.
- The reason is **False**.

### Summary
- **Assertion**: True
- **Reason**: False