Select number of species in which bond angle at nitrogen is greater than `120^(@)-`
`HNCS," " H_(3)CNCO, " "H_(3)SiNCS," "NO_(2)," " NO_(3)^(-)," "[BH_(2)(NH_(3))_(4)]^(+)," "N_(2)O`

Answer

To determine the number of species in which the bond angle at nitrogen is greater than 120 degrees, we will analyze each of the given species one by one.

### Step-by-Step Solution:

1. **HNCS (Thioformamide)**:
- Structure: Nitrogen (N) is bonded to one hydrogen (H), one carbon (C), and one sulfur (S) with a double bond to sulfur.
- Hybridization: The nitrogen has one lone pair and is involved in three bonds (one single bond with H, one double bond with C, and one double bond with S).
- Bond Angle: The presence of the lone pair increases the bond angle due to lone pair-bond pair repulsion. Thus, the bond angle is greater than 120 degrees.
- **Conclusion**: HNCS has a bond angle greater than 120°.

2. **H₃CNCO (Hydroxylamine)**:
- Structure: Nitrogen is bonded to three hydrogens and has a double bond with carbon, which is also bonded to oxygen.
- Hybridization: The nitrogen is sp² hybridized due to the presence of a double bond and three single bonds.
- Bond Angle: The bond angle between the groups is affected by the repulsion between the CH₃ and the C=O. Therefore, the bond angle is greater than 120 degrees.
- **Conclusion**: H₃CNCO has a bond angle greater than 120°.

3. **H₃SiNCS (Silicoformamide)**:
- Structure: Nitrogen is bonded to three hydrogens and has a double bond with carbon and sulfur.
- Hybridization: Similar to HNCS, nitrogen has one lone pair and is involved in multiple bonds.
- Bond Angle: The bond angle is influenced by the lone pair, making it greater than 120 degrees.
- **Conclusion**: H₃SiNCS has a bond angle greater than 120°.

4. **NO₂ (Nitrogen Dioxide)**:
- Structure: Nitrogen is bonded to two oxygen atoms, one with a double bond and one with a coordinate bond.
- Hybridization: The nitrogen has an odd electron and is sp² hybridized.
- Bond Angle: The bond angle is influenced by the lone electron and is greater than 120 degrees.
- **Conclusion**: NO₂ has a bond angle greater than 120°.

5. **NO₃⁻ (Nitrate Ion)**:
- Structure: Nitrogen is bonded to three oxygen atoms, one with a double bond and two with single bonds.
- Hybridization: The nitrogen is sp² hybridized and the molecule is trigonal planar.
- Bond Angle: The bond angle is exactly 120 degrees.
- **Conclusion**: NO₃⁻ does not have a bond angle greater than 120°.

6. **[BH₂(NH₃)₄]⁺ (Tetraammineboron)**:
- Structure: Nitrogen is bonded to three hydrogens and one boron.
- Hybridization: The nitrogen is sp³ hybridized.
- Bond Angle: The bond angle is approximately 107.8 degrees due to the lone pair.
- **Conclusion**: [BH₂(NH₃)₄]⁺ does not have a bond angle greater than 120°.

7. **N₂O (Nitrous Oxide)**:
- Structure: One nitrogen is triple bonded to another nitrogen and has a coordinate bond with oxygen.
- Hybridization: The nitrogen involved in the triple bond is sp hybridized.
- Bond Angle: The bond angle is 180 degrees.
- **Conclusion**: N₂O has a bond angle greater than 120°.

### Final Count:
The species with bond angles greater than 120 degrees are:
1. HNCS
2. H₃CNCO
3. H₃SiNCS
4. NO₂
5. N₂O

Thus, the total number of species with bond angles greater than 120 degrees is **5**.