Which set contains only covalently bonded molecules ?

Options

A. `BCl_(3),SiCl_(4),PCl_(3)`
B. `NH_(4)Br,N_(2)H_(4),HBr`
C. `I_(2),H_(2)S,NaI`
D. `Al,O_(3),As_(4)`

Explanation

To determine which set contains only covalently bonded molecules, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Covalent Bonds**:
- A covalent bond is formed by the sharing of electrons between two non-metals.
- In contrast, ionic bonds are formed by the complete transfer of electrons, typically between a metal and a non-metal.

2. **Analyzing the First Set**:
- **BCl3 (Boron Trichloride)**: Boron (B) and Chlorine (Cl) are both non-metals, so BCl3 is covalently bonded.
- **SiCl4 (Silicon Tetrachloride)**: Silicon (Si) and Chlorine (Cl) are both non-metals, so SiCl4 is also covalently bonded.
- **PCl3 (Phosphorus Trichloride)**: Phosphorus (P) and Chlorine (Cl) are both non-metals, so PCl3 is covalently bonded as well.
- **Conclusion**: All three compounds in the first set are covalently bonded.

3. **Analyzing the Second Set**:
- **Ammonium Bromide (NH4Br)**: This compound contains the ammonium ion (NH4+) and bromide ion (Br-), indicating ionic bonding.
- **N2H4 (Hydrazine)**: Both nitrogen (N) and hydrogen (H) are non-metals, so N2H4 is covalently bonded.
- **HBr (Hydrogen Bromide)**: This compound consists of H and Br, which also indicates ionic characteristics due to the presence of a hydrogen ion (H+) and bromide ion (Br-).
- **Conclusion**: Since NH4Br and HBr are ionic, this set does not contain only covalently bonded molecules.

4. **Analyzing the Third Set**:
- **I2 (Iodine)**: Iodine is a non-metal, and I2 forms a covalent bond.
- **H2S (Hydrogen Sulfide)**: Both hydrogen (H) and sulfur (S) are non-metals, so H2S is covalently bonded.
- **NaI (Sodium Iodide)**: Sodium (Na) is a metal and iodine (I) is a non-metal, indicating ionic bonding.
- **Conclusion**: Since NaI is ionic, this set does not contain only covalently bonded molecules.

5. **Analyzing the Fourth Set**:
- **Aluminum (Al)**: Aluminum is a metal and forms a metallic lattice, not covalent bonds.
- **Ozone (O3)**: Ozone consists of oxygen atoms, which are non-metals, so O3 is covalently bonded.
- **As4 (Arsenic)**: Arsenic is a non-metal and forms covalent bonds.
- **Conclusion**: Since aluminum is metallic, this set does not contain only covalently bonded molecules.

6. **Final Conclusion**:
- The only set that contains only covalently bonded molecules is the **first set**: BCl3, SiCl4, and PCl3.

### Answer:
The correct answer is **1** (BCl3, SiCl4, PCl3).