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

Explanation

To analyze the given assertion and reason, we will break down the statements step by step.

### Step 1: Analyze the Assertion
The assertion states that "Helium has the highest value of ionization 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 two electrons that are very close to the nucleus. The effective nuclear charge experienced by these electrons is quite high due to the presence of two protons in the nucleus. This strong attraction means that a significant amount of energy is required to remove an electron from helium, making its ionization energy the highest among all elements.

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

- **Explanation**: Electron affinity is defined as the energy change that occurs when an electron is added to a neutral atom in the gaseous state. For noble gases like helium, which already have a complete outer shell (1s²), the addition of an electron would lead to an unstable configuration. Therefore, noble gases generally have very low or even negative electron affinities, indicating that they do not favor gaining an electron. This means that the statement about helium having the highest electron affinity is incorrect.

### Step 3: Conclusion
- The assertion is **correct**: Helium does have the highest ionization energy among all elements.
- The reason is **incorrect**: Helium does not have the highest electron affinity; in fact, noble gases have the lowest electron affinity.

### Final Answer
The assertion is correct, but the reason is incorrect.

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