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 PH_(3) gt SbH_(3)`
C. `SbH_(2) gtAsH_(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 group 15 hydrides (NH3, PH3, AsH3, SbH3), we will analyze the molecular structures and bond angles of each hydride step by step.

### Step 1: Identify the Hydrides
The hydrides we are considering are:
- NH3 (Ammonia)
- PH3 (Phosphine)
- AsH3 (Arsine)
- SbH3 (Stibine)

### Step 2: Analyze NH3 (Ammonia)
- **Structure**: NH3 has a pyramidal structure due to the presence of a lone pair on nitrogen.
- **Hybridization**: The hybridization of nitrogen in NH3 is sp³.
- **Bond Angle**: The ideal bond angle for sp³ hybridization is approximately 109.5°. However, due to the lone pair-bond pair repulsion, the actual bond angle is reduced to about 107.3°.

### Step 3: Analyze PH3 (Phosphine)
- **Structure**: PH3 has a trigonal pyramidal structure, but the lone pair effect is less significant than in NH3.
- **Hybridization**: The hybridization is also sp³.
- **Bond Angle**: The bond angle in PH3 is around 93.5°, which is smaller than that of NH3 due to decreased lone pair repulsion and larger atomic size.

### Step 4: Analyze AsH3 (Arsine)
- **Structure**: AsH3 also has a similar pyramidal structure.
- **Hybridization**: The hybridization remains sp³.
- **Bond Angle**: The bond angle in AsH3 is approximately 91.8°, which is smaller than that of PH3 due to further increase in atomic size and decrease in electronegativity.

### Step 5: Analyze SbH3 (Stibine)
- **Structure**: SbH3 has a pyramidal structure similar to the previous hydrides.
- **Hybridization**: The hybridization is still sp³.
- **Bond Angle**: The bond angle in SbH3 is around 90.0°, which is the smallest among the group due to the largest atomic size and lowest electronegativity.

### Step 6: Sequence of Bond Angles
Based on the analysis, we can summarize the bond angles as follows:
- NH3: 107.3°
- PH3: 93.5°
- AsH3: 91.8°
- SbH3: 90.0°

### Conclusion
The correct sequence of decrease in bond angles for the group 15 hydrides is:
**NH3 > PH3 > AsH3 > SbH3**