Which of the following species contain only sigma bond?

Options

A. `SiCl_4`
B. `NO_3^-`
C. `HCN`
D. `SO_3^(2-) `

Answer

To determine which of the given species contain only sigma bonds, we will analyze each species one by one and draw their structures.

### Step-by-Step Solution:

1. **Identify the Species**: The species we need to analyze are SiCl₄, NO₃⁻, HCN, and SO₃.

2. **Draw the Structure of SiCl₄**:
- Silicon (Si) is the central atom.
- It is bonded to four chlorine (Cl) atoms.
- Each bond between Si and Cl is a single bond.
- **Conclusion**: All bonds in SiCl₄ are sigma bonds.

3. **Draw the Structure of NO₃⁻**:
- Nitrogen (N) is the central atom.
- It is bonded to three oxygen (O) atoms.
- One of the bonds is a double bond (N=O), which consists of one sigma bond and one pi bond.
- **Conclusion**: NO₃⁻ contains both sigma and pi bonds.

4. **Draw the Structure of HCN**:
- Carbon (C) is the central atom.
- It is bonded to one hydrogen (H) atom and one nitrogen (N) atom.
- The bond between C and N is a triple bond, which consists of one sigma bond and two pi bonds.
- **Conclusion**: HCN contains both sigma and pi bonds.

5. **Draw the Structure of SO₃**:
- Sulfur (S) is the central atom.
- It is bonded to three oxygen (O) atoms.
- Each bond between S and O is a double bond, which consists of one sigma bond and one pi bond.
- **Conclusion**: SO₃ contains both sigma and pi bonds.

6. **Final Evaluation**:
- From the analysis, only SiCl₄ contains only sigma bonds.
- The other species (NO₃⁻, HCN, SO₃) contain pi bonds.

### Answer:
**SiCl₄ is the only species that contains only sigma bonds.**