All carbon atoms are `sp^(2)` hybridised in

Options

A. `CH_(2)=C=CH_(2)`
B. 1, 3- butadiene
C. `CH-=C-C-=CH`
D. Cyclohexane

Answer

To determine which species has all carbon atoms that are `sp²` hybridized, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Hybridization**:
- Carbon has an electronic configuration of 1s² 2s² 2p², meaning it has 4 valence electrons.
- The hybridization of carbon can be determined by the number of sigma bonds it forms:
- **sp** hybridization: 2 sigma bonds
- **sp²** hybridization: 3 sigma bonds
- **sp³** hybridization: 4 sigma bonds

2. **Analyzing the Options**:
- **Option A: CH₂=CH-CH₂** (Propene)
- The structure has a double bond between the first two carbons.
- Each terminal carbon (CH₂) forms 3 sigma bonds (2 with H and 1 with C) and the middle carbon forms 2 sigma bonds (1 with each terminal C).
- Therefore, the terminal carbons are `sp²` hybridized, but the middle carbon is `sp` hybridized. **Not all carbons are sp²**.

- **Option B: 1,3-butadiene (C₄H₆)**
- The structure is H₂C=CH-CH=CH₂.
- Each carbon in 1,3-butadiene forms 3 sigma bonds (2 with H and 1 with C) for the terminal carbons and 3 sigma bonds for the internal carbons as well.
- All carbons here are forming 3 sigma bonds, thus they are all `sp²` hybridized. **This option is correct**.

- **Option C: H-C≡C-C≡C-H** (1,3-butadiene)
- Each carbon in the triple bonds forms 2 sigma bonds (1 with the adjacent carbon and 1 with H) and 2 pi bonds.
- Therefore, all carbons here are `sp` hybridized. **Not all carbons are sp²**.

- **Option D: Cyclohexane (C₆H₁₂)**
- Each carbon in cyclohexane forms 4 sigma bonds (2 with adjacent carbons and 2 with H).
- Therefore, all carbons are `sp³` hybridized. **Not all carbons are sp²**.

3. **Conclusion**:
- The only species where all carbon atoms are `sp²` hybridized is **1,3-butadiene (Option B)**.

### Final Answer:
**All carbon atoms are `sp²` hybridized in 1,3-butadiene.**

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