Which of the following is a Lewis acid ?

Options

A. `NaH`
B. `NF_(3)`
C. `PH_(3)`
D. `B(CH_(3))_(3)`

Explanation

To determine which of the given options is a Lewis acid, we need to understand the definition of a Lewis acid. A Lewis acid is a species that can accept an electron pair due to a deficiency of electrons.

Let's analyze each option step by step:

### Step 1: Analyze NaH
- **NaH** is an ionic compound composed of Na⁺ and H⁻ ions.
- Both ions have a complete octet, meaning there is no deficiency of electrons in NaH.
- **Conclusion**: NaH does not act as a Lewis acid.

### Step 2: Analyze NaF
- **NaF** is also an ionic compound, consisting of Na⁺ and F⁻ ions.
- The fluorine atom has a complete octet and does not have a deficiency of electrons.
- **Conclusion**: NaF does not act as a Lewis acid.

### Step 3: Analyze PH₃
- **PH₃** (phosphine) has phosphorus with 5 valence electrons.
- In PH₃, phosphorus shares 3 electrons with hydrogen, completing its octet.
- Since phosphorus has a complete octet, it does not have a tendency to accept additional electrons.
- **Conclusion**: PH₃ does not act as a Lewis acid.

### Step 4: Analyze B(Ph₃)₃
- **B(Ph₃)₃** (triphénylborane) consists of boron, which has 3 valence electrons.
- When boron bonds with three PH₃ groups, it shares electrons but only has 6 electrons around it.
- This leaves boron with a deficiency of 2 electrons, making it electron deficient.
- **Conclusion**: B(Ph₃)₃ behaves as a Lewis acid because it can accept an electron pair.

### Final Answer
The Lewis acid among the given options is **B(Ph₃)₃** (option 4).

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