Arrange the following oxides in order of increasing acidic character: `SO_3, Cl_2O_7, CaO and PbO_2. `

Explanation

To arrange the oxides `SO3`, `Cl2O7`, `CaO`, and `PbO2` in order of increasing acidic character, we need to analyze the oxidation states of the central atoms in each oxide and their corresponding acidic properties.

### Step-by-Step Solution:

1. **Identify the Oxidation States**:
- For `SO3`:
- Let the oxidation state of sulfur be \( x \).
- The equation is: \( x + 3(-2) = 0 \) (since there are three oxygen atoms, each with a -2 charge).
...