The correct order of acidic strength is

Options

A. `K_(2)O gt CaO gt MgO`
B. `CO_(2) gt N_(2)O_(5) gt SO_(3)`
C. `Na_(2)O gt MgO gt Al_(2)O_(3)`
D. `Cl_(2)O_(7) gt SO_(2) gt P_(4)O_(10)`

Explanation

To determine the correct order of acidic strength among the given options, we need to analyze the acidic properties of the compounds based on their oxidation states and positions in the periodic table.

### Step-by-Step Solution:

1. **Understanding Acidic Strength**:
Acidic strength generally increases across a period in the periodic table due to increasing electronegativity and oxidation states. Higher oxidation states typically correlate with stronger acids.

2. **Analyzing the Options**:
- **Option 1**: K2O > CaO > MgO
- These are oxides of alkali and alkaline earth metals. The acidic strength does not follow a clear trend based on periodic properties, so this option is not correct.

- **Option 2**: CO2 > N2O5 > SO3
- Here, we have oxides of non-metals. However, sulfur (in SO3) has a higher oxidation state than both carbon (in CO2) and nitrogen (in N2O5). Thus, SO3 should be the strongest acid, making this option incorrect.

- **Option 3**: Na2O > MgO > Al2O3
- This option also does not follow the expected trend. Al2O3 should have a higher acidic character due to its higher oxidation state compared to Na2O and MgO. Therefore, this option is incorrect.

- **Option 4**: Cl2O7 > SO2 > P4O10
- In this case, we have Cl2O7 (where chlorine is in a +7 oxidation state), SO2 (sulfur in +4 oxidation state), and P4O10 (phosphorus in +5 oxidation state). The order of acidic strength follows the trend of increasing oxidation state: Cl2O7 (+7) > SO2 (+4) > P4O10 (+5). Therefore, this option is correct.

3. **Conclusion**:
The correct order of acidic strength is **Cl2O7 > SO2 > P4O10**.

### Final Answer:
The correct order of acidic strength is **Cl2O7 > SO2 > P4O10** (Option 4).