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**:
- Covalent bonds are formed by the sharing of electrons between two non-metals.

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

3. **Analyzing the Second Set: NH4Br, N2H4, HBr**:
- **NH4Br (Ammonium Bromide)**:
- NH4+ is a cation and Br- is an anion. The bond between NH4+ and Br- is ionic.
- **N2H4 (Hydrazine)**:
- Both nitrogen (N) and hydrogen (H) are non-metals.
- Therefore, N2H4 is covalently bonded.
- **HBr (Hydrogen Bromide)**:
- H and Br are non-metals, but HBr dissociates into H+ and Br-, forming an ionic bond.
- **Conclusion for Second Set**: NH4Br is ionic, while N2H4 is covalent, and HBr is ionic. This set does not contain only covalently bonded molecules.

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

5. **Analyzing the Fourth Set: AlO3, O3, As4**:
- **AlO3 (Aluminum Oxide)**:
- Aluminum (Al) is a metal, and it forms ionic bonds with oxygen (O).
- **O3 (Ozone)**:
- Ozone consists of three oxygen atoms, which are non-metals, forming covalent bonds.
- **As4 (Arsenic)**:
- Arsenic (As) is a non-metal, and As4 forms covalent bonds.
- **Conclusion for Fourth Set**: AlO3 is ionic, while O3 and As4 are covalently bonded. This set does not contain only covalently bonded molecules.

### Final Conclusion:
After analyzing all the sets, we find that **only the first set (BCl3, SiCl4, PCl3)** contains only covalently bonded molecules.