A : `PF_5` and `IF_5` have similar shapes .
R : All the bond lengths are equal `PF_(5)`

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

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

**Assertion (A):** PF5 and IF5 have similar shapes.
**Reason (R):** All the bond lengths are equal in PF5.

### Step 1: Determine the shape of PF5
1. **Identify the central atom:** In PF5, the central atom is phosphorus (P).
2. **Count the valence electrons:** Phosphorus has 5 valence electrons.
3. **Count the monovalent atoms attached:** There are 5 fluorine (F) atoms attached to phosphorus.
4. **Calculate the hybridization using the formula:**
\[ H = \frac{1}{2} (V + M - C) \]
Here, V = 5 (valence electrons of P), M = 5 (number of F atoms), and C = 0 (no charge).
\[ H = \frac{1}{2} (5 + 5 - 0) = \frac{10}{2} = 5 \]
5. **Determine the hybridization:** The hybridization is sp³d, which corresponds to a trigonal bipyramidal geometry.

### Step 2: Determine the shape of IF5
1. **Identify the central atom:** In IF5, the central atom is iodine (I).
2. **Count the valence electrons:** Iodine has 7 valence electrons.
3. **Count the monovalent atoms attached:** There are 5 fluorine atoms attached to iodine.
4. **Calculate the hybridization using the formula:**
\[ H = \frac{1}{2} (V + M - C) \]
Here, V = 7 (valence electrons of I), M = 5 (number of F atoms), and C = 0 (no charge).
\[ H = \frac{1}{2} (7 + 5 - 0) = \frac{12}{2} = 6 \]
5. **Determine the hybridization:** The hybridization is sp³d², which corresponds to an octahedral geometry. However, since there are only 5 fluorine atoms, one position will be occupied by a lone pair, resulting in a square pyramidal shape.

### Step 3: Compare the shapes of PF5 and IF5
- **PF5:** Trigonal bipyramidal shape.
- **IF5:** Square pyramidal shape.

Since the shapes are different, the assertion is **false**.

### Step 4: Analyze the reason regarding bond lengths in PF5
1. In PF5, due to the trigonal bipyramidal geometry:
- There are two types of bonds: axial and equatorial.
- Axial bonds are longer than equatorial bonds.
2. Therefore, not all bond lengths in PF5 are equal.

Since the reason is also **false**, we conclude that both the assertion and reason are false.

### Final Conclusion
- **Assertion (A):** False
- **Reason (R):** False

Thus, the correct option is **B** (both assertion and reason are false).

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