The correct order of H-M-H bonds angle is :

Options

A. `NH_(3) lt PH_(3) lt SbH_(3) lt BiH_(3)`
B. `AsH_(3) lt SbH_(3) lt PH_(3) lt NH_(3)`
C. `NH_(3) lt PH_(3) lt BiH_(3) lt SbH_(3)`
D. `BiH_(3) lt SbH_(3) lt AsH_(3) lt PH_(3)`

Answer

To determine the correct order of H-M-H bond angles for the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements and Their Group**:
- The elements in question are nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). They belong to Group 15 of the periodic table.

2. **Consider the Molecular Geometry**:
- For each of these elements, we consider their hydrides: NH₃ (ammonia), PH₃ (phosphine), AsH₃ (arsine), SbH₃ (stibine), and BiH₃ (bismuthine). The geometry of these molecules is primarily influenced by the presence of lone pairs and bond pairs.

3. **Analyze the Size of the Atoms**:
- As we move down the group from nitrogen to bismuth, the atomic size increases. This is due to the addition of electron shells. Larger atoms have a greater distance between the nucleus and the bonding electrons.

4. **Evaluate Electronegativity**:
- Electronegativity decreases as we move down the group. Nitrogen is the most electronegative, while bismuth is the least. This affects how strongly the central atom can attract the bonding electrons.

5. **Consider Bond Pair-Bond Pair Repulsion**:
- In NH₃, the bond pairs are closer together due to the smaller size of nitrogen, leading to greater bond pair-bond pair repulsion. This results in a larger H-N-H bond angle (approximately 107°).
- In contrast, as we go down the group to PH₃, AsH₃, SbH₃, and BiH₃, the bond pair-bond pair repulsion decreases due to the larger atomic size and lower electronegativity, resulting in smaller bond angles.

6. **Determine the Bond Angle Order**:
- Based on the above analysis, the bond angles decrease as we move down the group:
- NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃
- Therefore, the correct order of H-M-H bond angles is:
- NH₃ (107°) > PH₃ (93.5°) > AsH₃ (91.2°) > SbH₃ (90°) > BiH₃ (approximately 90°).

7. **Final Conclusion**:
- The correct order of H-M-H bond angles is:
- NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃, which corresponds to option D in the given question.