Assertion : All F - S - F angle in `SF_(4)` are greater than `90^(@)` but less than `180^(@)`.
Reason :The lone pair -bond pair repulsion is weaker than bond pair -bond pair repulsion

Explanation

To solve the assertion and reason question regarding the angles in SF4 and the nature of lone pair-bond pair repulsion, we can break it down into steps:

### Step 1: Understand the Molecular Geometry of SF4
- **SF4** has a central sulfur atom bonded to four fluorine atoms.
- Sulfur has 6 valence electrons, and each fluorine has 7 valence electrons. Therefore, the total number of valence electrons in SF4 is:
\[ 6 + 4 \times 7 = 34 \text{ electrons} \]

### Step 2: Determine the Number of Bond Pairs and Lone Pairs
- To find the number of bond pairs and lone pairs, we divide the total number of valence electrons by 8 (since each bond pair uses 2 electrons):
\[ \frac{34}{2} = 17 \text{ pairs of electrons} \]
- Each bond pair contributes 1 to the count, and lone pairs contribute 1 as well. The quotient gives the number of bond pairs, and the remainder gives the number of lone pairs:
- Bond pairs = 4 (from 4 fluorine atoms)
- Lone pairs = 1 (since 34 - 8*4 = 2 electrons left, which means 1 lone pair)

### Step 3: Analyze the Shape of SF4
- The molecular geometry of SF4 is based on a trigonal bipyramidal arrangement due to the presence of 4 bond pairs and 1 lone pair.
- The lone pair occupies an equatorial position, which affects the bond angles.

### Step 4: Evaluate the Assertion
- The assertion states that all F-S-F angles in SF4 are greater than 90° but less than 180°.
- In reality, the axial F-S-F angles are slightly less than 90° due to the repulsion from the lone pair, while the equatorial F-S-F angles are approximately 120°.
- Thus, the assertion is **false**.

### Step 5: Evaluate the Reason
- The reason states that the lone pair-bond pair repulsion is weaker than bond pair-bond pair repulsion.
- This is incorrect; in fact, lone pair-bond pair repulsion is stronger than bond pair-bond pair repulsion. Therefore, the reason is also **false**.

### Conclusion
- Both the assertion and reason are false. Therefore, the correct answer is D: Assertion is false, Reason is false.

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