Among the following oxides, which is least acidic ?

Options

A. `Al_(2)O_(3)`
B. `B_(2)O_(3)`
C. `CO_(2)`
D. `NO_(2)`

Explanation

To determine which oxide is least acidic among the given options, we can follow these steps:

### Step 1: Identify the Oxides
Let's assume the oxides given are:
1. Al2O3 (Aluminium Oxide)
2. B2O3 (Boron Oxide)
3. CO2 (Carbon Dioxide)
4. NO2 (Nitrogen Dioxide)

### Step 2: Determine the Oxidation States
We need to find the oxidation states of the elements in each oxide.

- **For Al2O3**:
- Let the oxidation state of Al be \( x \).
- The equation becomes: \( 2x + 3(-2) = 0 \)
- Solving gives \( 2x - 6 = 0 \) → \( 2x = 6 \) → \( x = +3 \)

- **For B2O3**:
- Let the oxidation state of B be \( y \).
- The equation becomes: \( 2y + 3(-2) = 0 \)
- Solving gives \( 2y - 6 = 0 \) → \( 2y = 6 \) → \( y = +3 \)

- **For CO2**:
- Let the oxidation state of C be \( z \).
- The equation becomes: \( z + 2(-2) = 0 \)
- Solving gives \( z - 4 = 0 \) → \( z = +4 \)

- **For NO2**:
- Let the oxidation state of N be \( w \).
- The equation becomes: \( w + 2(-2) = 0 \)
- Solving gives \( w - 4 = 0 \) → \( w = +4 \)

### Step 3: Analyze Acidity Based on Oxidation State
According to Fajan's rule, higher oxidation states generally lead to higher covalent character, which correlates with increased acidity.

- **Oxidation States**:
- Al2O3: +3
- B2O3: +3
- CO2: +4
- NO2: +4

### Step 4: Compare Acidity
- CO2 and NO2 both have higher oxidation states (+4), suggesting they are more acidic than Al2O3 and B2O3.
- Between Al2O3 and B2O3, both have the same oxidation state (+3), but we need to consider the size of the cations.
- Aluminium (Al) is larger than Boron (B), leading to lower covalent character and thus lower acidity for Al2O3 compared to B2O3.

### Step 5: Conclusion
Based on the analysis:
- The order of acidity from highest to lowest is: NO2 > CO2 > B2O3 > Al2O3.
- Therefore, **Al2O3 is the least acidic oxide among the given options**.

### Final Answer:
**Al2O3 is the least acidic oxide.**

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