Which statement is not correct ?

Options

A. A sigma bond is weaker than a `pi`- bond.
B. A sigma bond is stroger than a `pi` -bond.
C. A double bond is stronger than a sigma bond.
D. A double bond is shorter than a single bond.

Answer

To determine which statement is not correct, we need to analyze each of the given options regarding sigma and pi bonds, as well as the properties of single and double bonds.

### Step-by-Step Solution:

1. **Understanding Sigma and Pi Bonds**:
- A **sigma bond** is formed by the head-on overlapping of atomic orbitals along the inter-nuclear axis, which results in a strong bond due to the direct overlap.
- A **pi bond** is formed by the side-to-side overlapping of p orbitals, which is generally weaker than a sigma bond because it has less effective overlap.

2. **Analyzing the Statements**:
- **Option 1**: "A sigma bond is weaker than a pi bond."
- This statement is incorrect because sigma bonds are generally stronger than pi bonds due to the nature of their overlap.

- **Option 2**: "A sigma bond is stronger than a pi bond."
- This statement is correct as sigma bonds have greater stability and strength compared to pi bonds.

- **Option 3**: "A double bond is stronger than a sigma bond."
- This statement is correct because a double bond consists of one sigma bond and one pi bond, making it stronger than a single sigma bond alone.

- **Option 4**: "A double bond is shorter than a single bond."
- This statement is also correct because a double bond pulls the bonded atoms closer together than a single bond, resulting in a shorter bond length.

3. **Conclusion**:
- The statement that is not correct is **Option 1**: "A sigma bond is weaker than a pi bond."

### Final Answer:
The statement that is not correct is: **"A sigma bond is weaker than a pi bond."**

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