Which of the following statement(s) is (are) correct regarding Lewis acids ?

Options

A. Molecules having a central atom with an incomplete octete in it can act as Lewis acids
B. Molecules in which atoms of dissimilar electronegativity are joined by multiple bonds can act as Lewis acids.
C. `SiF_(4) , PF_(5)` and `FeCl_(3)` are Lewis acids
D. Neutral species having at least one lone pair of electrons can act as Lewis acids

Answer

To determine which statements regarding Lewis acids are correct, we need to analyze each statement based on the definition and characteristics of Lewis acids. A Lewis acid is defined as a substance that can accept a pair of electrons.

### Step-by-Step Solution:

1. **Understanding Lewis Acids**:
- A Lewis acid is any substance that can accept an electron lone pair. This typically occurs in molecules where the central atom has an incomplete octet.

2. **Analyzing Statement 1**:
- **Statement**: Molecules having a central atom with an incomplete octet can act as Lewis acids.
- **Analysis**: This statement is correct. For example, boron trifluoride (BF3) has boron with only six electrons in its valence shell and can accept a lone pair of electrons.

3. **Analyzing Statement 2**:
- **Statement**: Molecules in which atoms of dissimilar electronegativity are joined by multiple bonds can act as Lewis acids.
- **Analysis**: This statement is also correct. An example is phosphorus trifluoride (PF3), where phosphorus has an incomplete octet and is bonded to highly electronegative fluorine atoms.

4. **Analyzing Statement 3**:
- **Statement**: SiF4, PF5, and FeCl3 are Lewis acids.
- **Analysis**: This statement is correct.
- SiF4 has silicon, which can expand its octet by utilizing vacant d-orbitals.
- PF5 has phosphorus that can also expand its octet.
- FeCl3 has iron with only six valence electrons, allowing it to accept a lone pair.

5. **Analyzing Statement 4**:
- **Statement**: Neutral species having at least one lone pair of electrons can act as Lewis acids.
- **Analysis**: This statement is incorrect. While species like ammonia (NH3) have lone pairs, they act as Lewis bases because they can donate their lone pair rather than accept one.

### Conclusion:
The correct statements regarding Lewis acids are:
- Statement 1: Correct
- Statement 2: Correct
- Statement 3: Correct
- Statement 4: Incorrect

Thus, the correct options are 1, 2, and 3.