In which of the following process, weaking of covalent bond take place :-

Options

A. Boiling of `H_(2)O`
B. Melting of KCN
C. Boiling of `CF_(4)`
D. Melting of `SiO_(2)`

Answer

To determine in which process the weakening of covalent bonds occurs, we need to analyze the given options and identify the presence of covalent bonds in each case.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- We need to check each option to see if it contains covalent bonds.
- **H2O (Water)**: Contains covalent bonds between hydrogen and oxygen.
- **KCl (Potassium Chloride)**: Contains ionic bonds, not covalent.
- **Si (Silicon)**: This is an elemental form and does not involve covalent bonding in the same way as compounds.
- **SiO2 (Silicon Dioxide)**: Contains covalent bonds between silicon and oxygen.

2. **Evaluate the Processes:**
- **Boiling of H2O**: When water boils, it transitions from a liquid to a gas. The covalent bonds between hydrogen and oxygen remain intact; however, the hydrogen bonds (which are weaker than covalent bonds) between water molecules are weakened. Therefore, there is no weakening of the covalent bond itself.
- **Melting of SiO2**: When silicon dioxide melts, it transitions from a solid to a molten state. In this process, the covalent bonds between silicon and oxygen atoms are weakened as the solid lattice structure breaks down.

3. **Conclusion:**
- Since the only process that involves the weakening of covalent bonds is the melting of SiO2, the correct answer is the melting of SiO2.

### Final Answer:
The process in which the weakening of covalent bonds takes place is **melting of SiO2**.

---