Which of the following statements is incorrect ?

Options

A. `A sigma` - bond is weaker than `a pi `-bond
B. There are four co-ordinate bonds in the `NH_(4)^(+)` ions
C. The covalent bond is directional in nature
D. HF is less polar than HCl

Answer

To determine which of the statements is incorrect, we will analyze each statement one by one.

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

- **Analysis:** Sigma bonds are formed by the head-to-head overlap of atomic orbitals, which results in a strong bond due to the direct overlap. In contrast, pi bonds are formed by the side-to-side overlap of p orbitals, which is generally weaker than sigma bonds. Therefore, this statement is incorrect.

### Step 2: Analyze Statement B
**Statement B:** There are four coordinate bonds in the NH4 ion.

- **Analysis:** The ammonium ion (NH4⁺) is formed when ammonia (NH3) reacts with a proton (H⁺). In NH3, nitrogen forms three covalent bonds with three hydrogen atoms and has one lone pair. When it forms NH4⁺, it donates its lone pair to bond with an additional H⁺, creating one coordinate bond. Therefore, this statement is also incorrect as there is only one coordinate bond in NH4⁺.

### Step 3: Analyze Statement C
**Statement C:** A covalent bond is a directional bond.

- **Analysis:** Covalent bonds are indeed directional because they form through the overlap of atomic orbitals in specific orientations, leading to a definite shape of the molecule. This statement is correct.

### Step 4: Analyze Statement D
**Statement D:** HF is less polar than HCl.

- **Analysis:** Fluorine is more electronegative than chlorine. In HF, the bond has a greater dipole moment because the electronegativity difference between H and F is larger than that between H and Cl. Therefore, HF is more polar than HCl, making this statement incorrect.

### Conclusion
The incorrect statements are A, B, and D. The only correct statement is C.

### Final Answer
The incorrect statements are:
- A: A sigma bond is weaker than a pi bond.
- B: There are four coordinate bonds in the NH4 ion.
- D: HF is less polar than HCl.