The C-C bond length of the following molecules is in the order:

(A) C₂H₆ > C₂H₄ > C₆H₆ > C₂H₂
(B) C₂H₂ < C₂H₄ < C₆H₆ < C₂H₆
(C) C₂H₆ < C₂H₂ < C₆H₆ < C₂H₄
(D) C₂H₄ < C₆H₆ < C₂H₂ < C₆H₆

To solve the question about the C-C bond lengths in the given molecules, we need to understand the nature of the bonding between the carbon atoms in each compound.

### Molecules involved:
1. **C₂H₆** (Ethane) – Single bond (C-C)
2. **C₂H₄** (Ethene) – Double bond (C=C)
3. **C₆H₆** (Benzene) – Resonance hybrid of alternating single and double bonds (delocalized π-bonds)
4. **C₂H₂** (Ethyne) – Triple bond (C≡C)

### Concept:
The bond order (the number of chemical bonds between two atoms) determines the bond length. As the bond order increases, the bond length decreases. The order of bonds and their lengths is:

- **Single bond (C-C)** > **Double bond (C=C)** > **Triple bond (C≡C)**

1. **C₂H₆ (Ethane)**: Carbon-carbon single bond, longest bond length.
2. **C₂H₄ (Ethene)**: Carbon-carbon double bond, shorter than a single bond.
3. **C₆H₆ (Benzene)**: The C-C bond length is intermediate due to resonance, where the bonds are between single and double in nature.
4. **C₂H₂ (Ethyne)**: Carbon-carbon triple bond, shortest bond length.

### Conclusion:
Thus, the order of C-C bond length is:
\[ \text{C}_2\text{H}_6 > \text{C}_2\text{H}_4 > \text{C}_6\text{H}_6 > \text{C}_2\text{H}_2 \]

### Correct answer:
\[ \boxed{\text{(B)}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{ < }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{ < }}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}{\text{ < }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}} \]