The molecule among the following that has the hybridization $sp^2, sp^2, sp, ext{ and } sp$ from left to rig

Question

The molecule among the following that has the hybridization $sp^2, sp^2, sp, 	ext{ and } sp$ from left to right atoms is:

Accepted Answer

1. **Hybridisation Rules:** The hybridisation of a carbon atom can be determined by the number of sigma ($\sigma$) bonds and lone pairs attached to it [NCERT 11th, Ch 12, Sec 12.3; NCERT 11th, Ch 4, Sec 4.6].
   - Carbon bonded to 4 atoms (4 single bonds) $\rightarrow sp^3$.
   - Carbon bonded to 3 atoms (1 double bond) $\rightarrow sp^2$.
   - Carbon bonded to 2 atoms (1 triple bond or 2 double bonds) $\rightarrow sp$.

2. **Analyze Option B ($CH_2 = CH - C \equiv CH$):**
   - **C1 (Left):** Forms a double bond with C2 and two single bonds with H. Steric number = 3. Hybridisation = **$sp^2$**.
   - **C2:** Forms a double bond with C1, a single bond with C3, and a single bond with H. Steric number = 3. Hybridisation = **$sp^2$**.
   - **C3:** Forms a single bond with C2 and a triple bond with C4. Steric number = 2. Hybridisation = **$sp$**.
   - **C4 (Right):** Forms a triple bond with C3 and a single bond with H. Steric number = 2. Hybridisation = **$sp$**.
   - **Sequence:** $sp^2, sp^2, sp, sp$. This matches the required sequence.

3. **Analyze Other Options:**
   - Option A ($HC \equiv C - C \equiv H$): All carbons are triple-bonded $\rightarrow sp, sp, sp, sp$.
   - Option C ($CH_2 = CH - CH = CH_2$): All carbons are double-bonded $\rightarrow sp^2, sp^2, sp^2, sp^2$.

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