The number of `sigma` and `pi`-bonds in but-1-en-3-yne are

Options

A. 5 sigma and 5 pi
B. 7 sigma and 3 pi
C. 8 sigma and 2 pi
D. 5 sigma and 4 pi.

Answer

To determine the number of sigma (σ) and pi (π) bonds in but-1-en-3-yne, we will first draw the structure of the compound and then count the bonds.

### Step-by-Step Solution:

1. **Draw the Structure of But-1-en-3-yne**:
- But-1-en-3-yne has four carbon atoms (C) and is characterized by a double bond (ene) at the first carbon and a triple bond (yne) starting from the third carbon.
- The structure can be represented as:
```
H2C=CH-C≡C-H
```
- Here, the first carbon (C1) is bonded to two hydrogens (H), the second carbon (C2) is bonded to one hydrogen and has a double bond with C1, the third carbon (C3) is bonded to C2 with a triple bond to C4, and C4 is bonded to one hydrogen.

2. **Identify the Types of Bonds**:
- **Single Bonds**: Each single bond contributes one sigma bond.
- **Double Bonds**: Each double bond contributes one sigma bond and one pi bond.
- **Triple Bonds**: Each triple bond contributes one sigma bond and two pi bonds.

3. **Count the Sigma Bonds**:
- C1 to C2 (single bond) = 1 σ bond
- C2 to C3 (double bond) = 1 σ bond
- C3 to C4 (triple bond) = 1 σ bond
- C1 to H (single bond) = 1 σ bond
- C2 to H (single bond) = 1 σ bond
- C3 to H (single bond) = 1 σ bond
- C4 to H (single bond) = 1 σ bond
- Total σ bonds = 7

4. **Count the Pi Bonds**:
- C2 to C3 (double bond) = 1 π bond
- C3 to C4 (triple bond) = 2 π bonds
- Total π bonds = 3

5. **Final Count**:
- Total σ bonds = 7
- Total π bonds = 3

### Conclusion:
The number of sigma and pi bonds in but-1-en-3-yne is:
- **7 sigma bonds and 3 pi bonds**.