Assertion: In CsF, salt, size of `Cs^(+)` is slight higher than size of `F^(-)`.
Reason: `Cs^(+)` is largest monoatomic cation and `F^(-)` is smallest anion.

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 given question, we need to analyze the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that in CsF (cesium fluoride), the size of the cation \( Cs^+ \) is slightly larger than the size of the anion \( F^- \).
- We need to determine whether this statement is true.

2. **Analyzing the Sizes of Ions**:
- Cesium (Cs) is located in Group 1 (alkali metals) of the periodic table. As we move down the group, the size of cations increases due to the addition of electron shells. Therefore, \( Cs^+ \) is indeed one of the largest monoatomic cations.
- Fluorine (F) is located in Group 17 (halogens). The size of anions generally increases as we move down the group, but \( F^- \) is the smallest anion because it has the highest effective nuclear charge relative to its size.

3. **Comparing the Sizes**:
- The size of \( Cs^+ \) is larger than that of neutral cesium due to the loss of an electron, which reduces the electron-electron repulsion. However, it remains large because it has a low effective nuclear charge compared to smaller cations.
- The size of \( F^- \) increases when it gains an electron due to electron-electron repulsion, but it is still smaller than \( Cs^+ \) because \( Cs^+ \) is from the sixth period while \( F^- \) is from the second period.

4. **Conclusion on Assertion**:
- The assertion is true because \( Cs^+ \) is indeed larger than \( F^- \).

5. **Understanding the Reason**:
- The reason states that \( Cs^+ \) is the largest monoatomic cation and \( F^- \) is the smallest anion.
- This statement is also true. \( Cs^+ \) is the largest cation due to its position in the periodic table, and \( F^- \) is the smallest anion due to its high effective nuclear charge.

6. **Conclusion on Reason**:
- The reason correctly explains why the assertion is true.

7. **Final Answer**:
- Both the assertion and the reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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