Which of the following statement is wrong ? .

Options

A. A sigma bond is shorter than a pi-bond .
B. Bond energies of sigma and pi bonds are of the order of 264 and `347 kJ mo1^(-1)` .
C. Free rotation of atoms about sigma bond is allowed but not in case of a-pi bond .
D. A sigma-bond determines the direction between C-atoms but a pi-bond has no primary effect which leads to bonding .

Explanation

To determine which statement is wrong among the given options, we will analyze each statement regarding sigma and pi bonds.

### Step 1: Analyze Statement A
**Statement A**: A sigma bond is shorter than a pi bond.

- **Explanation**: A sigma bond is formed by the head-on overlap of orbitals, which allows for maximum overlap. This results in a stronger bond that is generally shorter than a pi bond, which is formed by the side-to-side overlap of p orbitals. Therefore, this statement is **correct**.

### Step 2: Analyze Statement B
**Statement B**: Bond energies of sigma and pi bonds are of the order of 264 and 347 kilojoules per mole.

- **Explanation**: The bond energy of a sigma bond is typically higher than that of a pi bond. The correct values are approximately 347 kJ/mol for a sigma bond and 264 kJ/mol for a pi bond. Since this statement reverses the correct values, it is **wrong**.

### Step 3: Analyze Statement C
**Statement C**: Rotation of atoms about a sigma bond is allowed, but not in the case of a pi bond.

- **Explanation**: This statement is true. In a sigma bond, free rotation is possible because the bond is formed by the overlap of orbitals that allows for rotational freedom. In contrast, a pi bond restricts rotation due to the presence of the overlapping p orbitals. Therefore, this statement is **correct**.

### Step 4: Analyze Statement D
**Statement D**: A sigma bond determines the direction between carbon atoms, but a pi bond has no primary effect which leads to bonding.

- **Explanation**: This statement is also true. Sigma bonds are formed by hybridized orbitals, which have a directional character, thus determining the geometry of the molecule. Pi bonds, formed by unhybridized p orbitals, do not contribute to the directionality in the same way. Therefore, this statement is **correct**.

### Conclusion
After analyzing all statements, we find that **Statement B** is the wrong statement.

### Final Answer
The wrong statement is **Option B**.

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