Which of the following cannot behave like a Lewis acid ?

Options

A. `CO_3^(2-)`
B. `Zn^(2+)`
C. `SO_3`
D. `SiCl_4`

Answer

To determine which of the following cannot behave like a Lewis acid, we first need to understand the definition of a Lewis acid. A Lewis acid is defined as a substance that can accept an electron pair from a Lewis base.

### Step-by-step solution:

1. **Identify the options**: We need to analyze the given options to see which one cannot behave as a Lewis acid. The options are:
- A) CO3^2-
- B) SiCl4
- C) SO3
- D) Zn^2+

2. **Analyze CO3^2- (Carbonate ion)**:
- The carbonate ion (CO3^2-) has a central carbon atom bonded to three oxygen atoms.
- The carbon atom in CO3^2- does not have any vacant d-orbitals because it is in the second period of the periodic table.
- Additionally, the carbon atom cannot expand its octet, as it is limited to holding a maximum of 8 electrons.
- Therefore, CO3^2- cannot accept additional electrons and cannot behave as a Lewis acid.

3. **Analyze SiCl4 (Silicon tetrachloride)**:
- Silicon (Si) is in the third period and has vacant d-orbitals.
- SiCl4 can accept an electron pair, making it a Lewis acid.

4. **Analyze SO3 (Sulfur trioxide)**:
- Sulfur (S) is also in the third period and has vacant d-orbitals.
- SO3 can accept an electron pair, thus it behaves as a Lewis acid.

5. **Analyze Zn^2+ (Zinc ion)**:
- Zinc (Zn) has vacant d-orbitals and can also accept electron pairs.
- Therefore, Zn^2+ can act as a Lewis acid.

6. **Conclusion**:
- Among the options, only CO3^2- cannot behave like a Lewis acid because it lacks the ability to accept electrons due to the absence of vacant d-orbitals and the inability to expand its octet.

### Final Answer:
The option that cannot behave like a Lewis acid is **A) CO3^2-**.