Which of the following is the correct order for increasing bond angle ?

Options

A. `NH_3 lt PH_3 lt AsH_3 lt SbH_3`
B. `H_2O lt OF_2 lt Cl_2O`
C. `H_3Te^(+) lt H_3Se^(+) lt H_3S^(+) lt H_3O^+`
D. `BF_3 lt BCl_3 lt BBr_3 lt BI_3`

Answer

To determine the correct order for increasing bond angles among the given options, we need to analyze the bond angles based on the electronegativity of the central atom and the side atoms, as well as the presence of lone pairs. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Factors Affecting Bond Angles
- **Electronegativity of Central Atom**: If the side atoms are the same, the bond angle is directly proportional to the electronegativity of the central atom.
- **Electronegativity of Side Atoms**: If the central atom is the same, the bond angle is inversely proportional to the electronegativity of the side atoms.
- **Lone Pairs**: The presence of lone pairs on the central atom can also affect the bond angle, typically reducing it due to repulsion.

### Step 2: Analyze the Given Options
1. **Option 1**: Compare NH3 (ammonia) and PH3 (phosphine).
- Nitrogen is more electronegative than phosphorus, hence NH3 will have a larger bond angle than PH3. This option is incorrect.

2. **Option 2**: Compare H2O (water) and HF (hydrogen fluoride).
- Here, the central atom is oxygen. Since fluorine is more electronegative than hydrogen, the bond angle in HF should be less than in H2O. However, HF is incorrectly placed in the middle. This option is also incorrect.

3. **Option 3**: Compare H2S, H2Se, and H2Te.
- All have the same central atom (group 16 elements). As we move down the group, electronegativity decreases, leading to an increase in bond angle. Thus, H2S > H2Se > H2Te. This option is correct.

4. **Option 4**: Compare BF3 and BCl3.
- Boron is electron deficient and has no lone pairs. Both BF3 and BCl3 have a trigonal planar geometry, leading to equal bond angles. This statement is false.

### Conclusion
The correct order for increasing bond angle is represented in **Option 3**: H2Te < H2Se < H2S.