Which of the following statements are incorrect ?

Options

A. `SO_(3)` is a stronger oxidising agent and more acidic than `SO_(2)`.
B. Selenium forms only two oxoacids i.e., selenous acid `(H_(2)SeO_(3))` and selenic acid `(H_(2)SeO_(4))`.
C. The acidic strength and oxidising power of oxoacids is greater in +6 oxidation state than in +4 oxidation state.
D. The thermal stability of oxides of group 16 elements decreases in the order : `SO_(2) gt SeO_(2) gt TeO_(2) gt PoO_(2)`

Explanation

To determine which of the given statements is incorrect, we will analyze each statement step by step.

### Step 1: Analyze Statement 1
**Statement:** SO3 is a stronger oxidizing agent and more acidic than SO2.

- **Oxidizing Agent:** In SO3, sulfur has an oxidation state of +6, while in SO2, sulfur has an oxidation state of +4. Higher oxidation states typically correspond to stronger oxidizing agents. Therefore, SO3 is indeed a stronger oxidizing agent than SO2.

- **Acidity:** The acidity of oxoacids generally increases with the number of oxygen atoms. Since SO3 has more oxygen atoms than SO2, it is also more acidic.

**Conclusion:** This statement is correct.

### Step 2: Analyze Statement 2
**Statement:** Selenium forms only two oxoacids: selenous acid and selenic acid.

- **Oxoacids of Selenium:** Selenium forms two primary oxoacids: H2SeO3 (selenous acid) and H2SeO4 (selenic acid).

**Conclusion:** This statement is correct.

### Step 3: Analyze Statement 3
**Statement:** The acidic strength and oxidizing power of oxyacids is greater in the +6 oxidation state than in the +4 oxidation state.

- **Comparison of Oxidation States:** As established earlier, oxyacids with higher oxidation states (like +6) are generally stronger acids and stronger oxidizing agents compared to those with lower oxidation states (like +4).

**Conclusion:** This statement is correct.

### Step 4: Analyze Statement 4
**Statement:** The thermal stability of oxides of group 16 decreases in order from SO2 to TeO2 to PoO2.

- **Thermal Stability Trend:** In group 16, the thermal stability of oxides generally increases down the group. This means that the thermal stability of PoO2 should be greater than that of TeO2, which in turn should be greater than that of SO2.

**Conclusion:** This statement is incorrect because it claims that the thermal stability decreases, which contradicts the established trend.

### Final Answer
The incorrect statement is **Statement 4**.

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