The correct sequence of decrease in the bond angles of the following hydrides is

Options

A. `NH_3 gt Ph_3 gt AsH_3 gt SbH_3`
B. `NH_3 gt AsH_3 gt SbH_3`
C. `SbH_3 gt AsH_3 gt PH_3 gt NH_3`
D. `PH_3 gt NH_3 gt AsH_3 gt SbH_3`

Answer

To determine the correct sequence of decrease in the bond angles of the hydrides NH3, PH3, AsH3, and SbH3, we can follow these steps:

### Step 1: Identify the hybridization of each hydride
- **NH3 (Ammonia)**: The nitrogen atom undergoes sp3 hybridization, resulting in a tetrahedral geometry. The ideal bond angle for a tetrahedral structure is 109.5°, but due to the presence of a lone pair, the bond angle is reduced to approximately 104°.
- **PH3 (Phosphine)**: The phosphorus atom also undergoes sp3 hybridization, but the bond angle is further reduced to about 93.5° due to the larger size of phosphorus and the presence of a lone pair.
- **AsH3 (Arsenic Hydride)**: Similar to PH3, arsenic also has sp3 hybridization, but the bond angle is even smaller, around 91.8°.
- **SbH3 (Stibine)**: The bond angle in SbH3 is the smallest, approximately 90°, due to the larger atomic size of antimony compared to the other elements.

### Step 2: Compare the bond angles
From the analysis:
- NH3 has the largest bond angle (approximately 104°).
- PH3 has a smaller bond angle (approximately 93.5°).
- AsH3 has an even smaller bond angle (approximately 91.8°).
- SbH3 has the smallest bond angle (approximately 90°).

### Step 3: Arrange the hydrides in order of decreasing bond angles
Based on the bond angles identified:
1. NH3 (104°)
2. PH3 (93.5°)
3. AsH3 (91.8°)
4. SbH3 (90°)

Thus, the correct sequence of decrease in bond angles is:
**NH3 > PH3 > AsH3 > SbH3**

### Final Answer
The correct sequence of decrease in the bond angles of the given hydrides is: **NH3 > PH3 > AsH3 > SbH3**.