Which substance has the highest melting point ?

Options

A. CO
B. `CO_(2)`
C. `SiO_(2)`
D. `P_(2)O_(5)`

Explanation

To determine which substance has the highest melting point among the given options (A-CO, B-CO2, C-SiO2, D-P2O5), we can analyze the nature of each compound and their bonding structures.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- A: CO (Carbon Monoxide)
- B: CO2 (Carbon Dioxide)
- C: SiO2 (Silicon Dioxide)
- D: P2O5 (Diphosphorus Pentoxide)

2. **Determine the Type of Bonding**:
- All four compounds are covalent in nature. However, they differ in their structural arrangements.
- CO and CO2 are molecular compounds that form molecular lattices.
- SiO2 forms a covalent network structure (3D network).
- P2O5 also forms a molecular lattice.

3. **Understand Molecular vs. Covalent Lattice**:
- **Molecular Lattice**: In molecular lattices (like CO, CO2, and P2O5), the molecules are held together by weaker intermolecular forces (like Van der Waals forces).
- **Covalent Lattice**: In a covalent lattice (like SiO2), atoms are bonded together by strong covalent bonds in a three-dimensional network.

4. **Compare Stability and Melting Points**:
- The stability of a lattice structure is directly related to its melting point. A more stable lattice will have a higher melting point.
- Since SiO2 has a covalent network structure, it is more stable compared to the molecular lattices of CO, CO2, and P2O5.

5. **Conclusion**:
- Based on the analysis, SiO2 (Silicon Dioxide) has the highest melting point among the options provided.

### Final Answer:
The substance with the highest melting point is **C-SiO2**.

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