Correct sequence of bond length is:

Options

A. `HC -= CH gt H_2 C = CH_2 gt H_3 C - CH_3`
B. `H_2 C = CH_2 gt HC -= CH gt H_3 C - CH_3`
C. `H_3 C - CH_3 gt H_2 C = CH_2 gt HC -= CH`
D. `H_3 C - CH_3 gt HC -= HC gt H_2 C = CH_2`

Answer

To determine the correct sequence of bond lengths among alkanes, alkenes, and alkynes, we need to consider the types of bonds present in each category and their respective hybridizations.

### Step-by-Step Solution:

1. **Identify the Types of Bonds**:
- Alkanes (e.g., ethane, H3C-CH3) contain single bonds (sigma bonds).
- Alkenes (e.g., ethylene, H2C=CH2) contain double bonds (one sigma bond and one pi bond).
- Alkynes (e.g., acetylene, HC≡CH) contain triple bonds (one sigma bond and two pi bonds).

2. **Determine Hybridization**:
- In alkanes, the carbon atoms are sp³ hybridized (four sigma bonds).
- In alkenes, the carbon atoms are sp² hybridized (three sigma bonds and one pi bond).
- In alkynes, the carbon atoms are sp hybridized (two sigma bonds and two pi bonds).

3. **Analyze S-Character**:
- The s-character increases with the type of hybridization:
- sp³ (alkane) = 25% s-character
- sp² (alkene) = 33% s-character
- sp (alkyne) = 50% s-character
- Higher s-character means the electrons are closer to the nucleus, leading to shorter bond lengths.

4. **Compare Bond Strength and Length**:
- As the s-character increases, the bond strength increases, and consequently, the bond length decreases.
- Therefore, the order of bond lengths from longest to shortest is:
- Alkanes (longest bond length)
- Alkenes (intermediate bond length)
- Alkynes (shortest bond length)

5. **Conclusion**:
- The correct sequence of bond lengths is:
**Alkane > Alkene > Alkyne**.

### Final Answer:
The correct sequence of bond length is: **Alkane > Alkene > Alkyne**.