Which of thef following is not Lewis acid

Options

A. `BF_(3)`
B. `AlCl_(3)`
C. `FeCl_(3)`
D. `PH_(3)`

Explanation

To determine which of the following options is not a Lewis acid, we 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 means that a Lewis acid must have at least one vacant orbital available to accept electrons.

Let's analyze the options provided in the question step by step:

### Step 1: Identify the Lewis Acids
1. **BF3 (Boron Trifluoride)**:
- Boron has an electronic configuration of 1s² 2s² 2p¹.
- In its ground state, it does not have a complete octet.
- Upon excitation, one of the 2s electrons can be promoted to the 2p orbital, leaving a vacant orbital available to accept a lone pair of electrons.
- Therefore, BF3 is a Lewis acid.

2. **AlCl3 (Aluminum Chloride)**:
- Aluminum has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p¹.
- Similar to BF3, it can also promote an electron to create a vacant orbital.
- Thus, AlCl3 can accept a lone pair of electrons and is also a Lewis acid.

3. **FeCl3 (Iron(III) Chloride)**:
- Iron in FeCl3 has an electronic configuration that allows it to have vacant orbitals.
- It can accept electron pairs from Lewis bases, making it a Lewis acid.

### Step 2: Analyze the Non-Lewis Acid
4. **PH3 (Phosphine)**:
- Phosphorus has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p³.
- In PH3, phosphorus has one lone pair of electrons and does not have vacant orbitals available to accept additional electron pairs.
- Instead, PH3 behaves as a Lewis base because it can donate its lone pair of electrons.

### Conclusion
Based on the analysis, PH3 is the only compound among the options that does not act as a Lewis acid. Therefore, the answer to the question is:

**PH3 is not a Lewis acid.**

### Final Answer:
**D. PH3 is not a Lewis acid.**

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