How many of the following order of bond energies are correct.
(i)` C-C gt Si-Si` , (ii) `C-O gt Si-O` , (iii) `C-FgtSi-F` , (iv) `C-FgtSi-F` , (v) `C-HgtSi-H` , (vi) `Si-Cl gt C-Cl` (vii) `Si-SigtC-Si` , (viii) `C-BrgtSi-Br`

Answer

To determine how many of the given orders of bond energies are correct, we will analyze each option step by step.

### Step 1: Analyze the bond energy orders

1. **(i) C-C > Si-Si**
- Carbon (C) has a smaller atomic size and a higher bond strength compared to silicon (Si). Therefore, C-C bond is stronger than Si-Si bond.
- **Conclusion:** Correct

2. **(ii) C-O > Si-O**
- Both carbon and oxygen are in the second period, while silicon is in the third period. The C-O bond is stronger due to the smaller size of carbon compared to silicon.
- **Conclusion:** Correct

3. **(iii) C-F > Si-F**
- Carbon (2p) forms a bond with fluorine (2p), while silicon (3p) forms a bond with fluorine (2p). The bond strength decreases as the size of the atom increases. Therefore, C-F is stronger than Si-F.
- **Conclusion:** Correct

4. **(iv) C-F > Si-F** (This is a repeat of iii)
- **Conclusion:** Correct

5. **(v) C-H > Si-H**
- Carbon (2p) has a smaller size compared to silicon (3p), resulting in a stronger bond with hydrogen. Therefore, C-H is stronger than Si-H.
- **Conclusion:** Correct

6. **(vi) Si-Cl > C-Cl**
- Silicon and chlorine are both in the third period, while carbon is in the second period. The bond strength is higher for C-Cl due to the smaller size of carbon.
- **Conclusion:** Incorrect

7. **(vii) Si-Si > C-Si**
- The Si-Si bond involves 3p-3p overlap, while C-Si involves 2p-3p overlap. The 2p-3p overlap is weaker than 3p-3p overlap, making C-Si stronger.
- **Conclusion:** Incorrect

8. **(viii) C-Br > Si-Br**
- Similar to the previous reasoning, C-Br bond involves 2p-4p overlap, while Si-Br involves 3p-4p overlap. The C-Br bond is stronger due to the smaller size of carbon.
- **Conclusion:** Correct

### Summary of Results
- Correct options: (i), (ii), (iii), (iv), (v), (viii)
- Incorrect options: (vi), (vii)

### Final Count of Correct Orders
Out of the eight given orders, **six** are correct.