The heavier members of `13` and `14` groups besides the group
oxidation state also show another oxidation state. Down the group `(darr)`, the stability of higher oxidation state increases. This concept which is commonly called inert pair effect has been used to explain many physical and chemical properties of the element of these
groups.
Which of the following acts as the strongest acid ?

Options

A. `Tl_(2)O_(3)`
B. `SnO_(2)`
C. `PbO_(2)`
D. `CO_(2)`

Explanation

To determine which of the following acts as the strongest acid among the given options, we need to analyze the acidic nature of the oxides of the heavier members of groups 13 and 14, considering the inert pair effect and the trends in acidity down the groups.

### Step-by-Step Solution:

1. **Understand the Groups**:
- Group 13 includes elements like Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).
- Group 14 includes elements like Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), and Lead (Pb).

2. **Identify the Oxides**:
- The oxides mentioned in the question are:
- Thallium oxide: Tl2O3 (from Group 13)
- Tin oxide: SnO2 (from Group 14)
- Lead oxide: PbO2 (from Group 14)
- Carbon dioxide: CO2 (from Group 14)

3. **Analyze the Acid-Base Character**:
- For Group 13, as we move down the group, the basic character of oxides increases. Therefore, Tl2O3 is more basic and less acidic.
- For Group 14, the acidic character of oxides generally decreases down the group. However, oxides in higher oxidation states tend to be more acidic.

4. **Determine the Acidic Nature of Each Oxide**:
- **Tl2O3**: This oxide is basic due to thallium's lower oxidation state.
- **SnO2**: This oxide is amphoteric, meaning it can act as both an acid and a base.
- **PbO2**: This oxide is also amphoteric but less acidic than SnO2.
- **CO2**: This oxide is acidic because carbon in CO2 is in a higher oxidation state (+4) and forms an acidic oxide.

5. **Conclusion**:
- Among the options, CO2 is the strongest acid because it is a non-metal oxide that forms an acidic solution when dissolved in water, while the other oxides are either basic or amphoteric.

### Final Answer:
The strongest acid among the given options is **CO2**.

---