Point out the species which acts as Lewis acids.

Options

A. `Mg^(2+), H_2O, NH_3`
B. `NH_3, OH^-, Co^(3+)`
C. `AlCl_3, Co^(3+), Mg^(2+)`
D. `AlCl_3, H_2O, Co^(3+)`

Answer

To identify the species that act as Lewis acids, we first need to understand the definition of a Lewis acid. A Lewis acid is defined as a substance that can accept a pair of electrons to form a covalent bond. This typically occurs when the species has a vacant orbital that can accommodate the incoming electron pair.

### Step-by-Step Solution:

1. **Definition of Lewis Acid**:
- A Lewis acid is a chemical species that can accept an electron pair from a Lewis base. This means that Lewis acids must have vacant orbitals available for bonding.

2. **Characteristics of Lewis Acids**:
- Lewis acids often include metal cations, electron-deficient molecules, or compounds with incomplete octets. They can accept lone pairs of electrons from Lewis bases.

3. **Examples of Lewis Acids**:
- **Aluminum Chloride (AlCl3)**:
- Aluminum in AlCl3 has only six electrons in its valence shell (it is electron-deficient), making it a good Lewis acid as it can accept electron pairs.
- **Metal Ions (e.g., Mg²⁺, Co³⁺)**:
- Metal cations like Mg²⁺ and Co³⁺ can also act as Lewis acids because they have vacant orbitals and can accept electron pairs from Lewis bases.
- **Other Electron-Deficient Molecules**:
- Compounds that are electron-deficient or have incomplete octets can also act as Lewis acids.

4. **Conclusion**:
- The species that act as Lewis acids in the context of the question include AlCl3, Mg²⁺, and Co³⁺. These species have vacant orbitals and can accept electron pairs.

### Summary of Lewis Acids Identified:
- **AlCl3** (Aluminum Chloride)
- **Mg²⁺** (Magnesium Ion)
- **Co³⁺** (Cobalt Ion)