Which of the following species acts as a Lewis acid and also as a Lewis base ?

Options

A. `SO_(2)`
B. `SCI_(4)`
C. both `SO_(2)` and `SCI_(4)`
D. `SO_(3)`

Answer

To determine which of the given species acts as both a Lewis acid and a Lewis base, we need to understand the definitions of Lewis acids and bases:

1. **Lewis Acid**: A species that can accept a pair of electrons.
2. **Lewis Base**: A species that can donate a pair of electrons.

Now, let's analyze each option step by step:

### Step 1: Analyze SO2 (Sulfur Dioxide)
- **Structure**: SO2 has a sulfur atom bonded to two oxygen atoms with a double bond and has one lone pair of electrons on the sulfur atom.
- **Lewis Base Behavior**: The lone pair of electrons on sulfur can be donated, allowing SO2 to act as a Lewis base.
- **Lewis Acid Behavior**: SO2 has an empty d orbital which can accept a pair of electrons, allowing it to act as a Lewis acid.

### Conclusion for SO2:
SO2 can act as both a Lewis acid and a Lewis base.

### Step 2: Analyze SCl4 (Sulfur Tetrachloride)
- **Structure**: SCl4 has a sulfur atom bonded to four chlorine atoms and has one lone pair of electrons on the sulfur atom.
- **Lewis Base Behavior**: The lone pair of electrons can be donated, allowing SCl4 to act as a Lewis base.
- **Lewis Acid Behavior**: SCl4 also has an empty d orbital which can accept a pair of electrons, allowing it to act as a Lewis acid.

### Conclusion for SCl4:
SCl4 can act as both a Lewis acid and a Lewis base.

### Step 3: Analyze SO3 (Sulfur Trioxide)
- **Structure**: SO3 has a sulfur atom bonded to three oxygen atoms with double bonds and does not have any lone pairs of electrons.
- **Lewis Acid Behavior**: SO3 has an incomplete octet around the sulfur atom, which means it has a tendency to accept electrons to complete its octet. Thus, it can act as a Lewis acid.
- **Lewis Base Behavior**: SO3 does not have any lone pairs to donate, so it cannot act as a Lewis base.

### Conclusion for SO3:
SO3 can only act as a Lewis acid, not a Lewis base.

### Final Answer:
Both SO2 and SCl4 can act as both Lewis acids and Lewis bases. Therefore, the correct option is **C) both SO2 and SCl4**.

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