Which of the following reactions of benzene does not account for the three `C=C` bonds in the molecule-
(a) Benzene`+Br_(2)underset("conc". H_(2)SO_(4))overset(FeBr_(3))rarr"bromobenzene"+HBr`
(b) Benzene `+HNO_(3)rarr"nitrobenzen.e+H_(2)O`
(c) Benzene`+3O_(3)rarr` Triozonide
(d) Benzene `+3H_(2)overset(Ni)rarr`cyclohexane

Options

A. a,c
B. b,d
C. b,c,d
D. a,b

Explanation

To solve the question regarding which reaction of benzene does not account for the three carbon-carbon bonds in the molecule, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Analyze Reaction (a)**:
- **Reaction**: Benzene + Br₂ (in the presence of conc. H₂SO₄ and FeBr₃) → Bromobenzene + HBr.
- **Mechanism**: This is an electrophilic substitution reaction. The bromine molecule (Br₂) interacts with the catalyst (FeBr₃) to form an electrophile (Br⁺). The benzene ring, which has alternating double bonds, will undergo substitution where one of the hydrogen atoms is replaced by a bromine atom.
- **Conclusion**: No carbon-carbon double bonds are broken in this reaction. Therefore, this reaction does not account for the three C=C bonds in benzene.

2. **Analyze Reaction (b)**:
- **Reaction**: Benzene + HNO₃ (in the presence of H₂SO₄) → Nitrobenzene + H₂O.
- **Mechanism**: Similar to reaction (a), this is also an electrophilic substitution reaction. The nitronium ion (NO₂⁺) acts as the electrophile. The benzene ring undergoes substitution, replacing one hydrogen atom with a nitro group (NO₂).
- **Conclusion**: Again, there is no cleavage of carbon-carbon double bonds. This reaction also does not account for the three C=C bonds in benzene.

3. **Analyze Reaction (c)**:
- **Reaction**: Benzene + 3O₃ → Triozonide.
- **Mechanism**: This reaction involves the ozonolysis of benzene, where ozone (O₃) reacts with the double bonds in benzene. The reaction leads to the cleavage of the carbon-carbon double bonds and the formation of ozonides.
- **Conclusion**: This reaction does account for the cleavage of carbon-carbon bonds, as the double bonds are broken to form the ozonide.

4. **Analyze Reaction (d)**:
- **Reaction**: Benzene + 3H₂ (in the presence of Ni) → Cyclohexane.
- **Mechanism**: This is a hydrogenation reaction where benzene is converted into cyclohexane. The hydrogenation process involves the addition of hydrogen across the double bonds, effectively breaking the carbon-carbon double bonds.
- **Conclusion**: This reaction also accounts for the breaking of carbon-carbon bonds, as all the double bonds in benzene are converted to single bonds.

### Final Conclusion:
The reactions that do not account for the three C=C bonds in benzene are:
- (a) Benzene + Br₂ → Bromobenzene
- (b) Benzene + HNO₃ → Nitrobenzene

Thus, the correct answer is **(a) and (b)**.