For p-block elements (like Group 16), the non-metal oxides are typically acidic, and the oxides where the element is in an intermediate oxidation state (like $+4$ for $\text{SO}_2$ and $\text{SeO}_2$) can act as both oxidizing and reducing agents. The physical state of oxides often changes down a group due to size and polarizability (e.g., $\text{SO}_2$ is a gas, $\text{SeO}_2$ is a solid).
Step 1: Analyze statement (A): $\text{TeO_2$ is an oxidizing agent.}
Tellurium is in Group 16. In $\text{TeO}_2$, the oxidation state of $\text{Te}$ is $+4$. $\text{Te}$ can be oxidized to $+6$ ($\text{TeO}_3$) or reduced to $+2$ or $0$. Since $\text{Te}$ can be oxidized, $\text{TeO}_2$ can act as a reducing agent. However, $\text{TeO}_2$ is a stable intermediate state and can also be reduced to $\text{Te}$ metal, meaning it can also act as an oxidizing agent. Its dominant behavior depends on the reaction conditions, but the statement that it is an oxidizing agent is chemically plausible (e.g., in reactions where a stronger reducing agent is present). The key implies this is correct, which is true because it can be reduced from $\text{Te}^{+4}$ to $\text{Te}^0$.
Step 2: Analyze statement (B): $\text{SeO_3$ is acidic in nature.}
Selenium ($\text{Se}$) is a non-metal in Group 16. Its highest oxidation state oxide, $\text{SeO}_3$, is $\text{Se}^{+6}$. Non-metal oxides are typically acidic. $\text{SeO}_3$ dissolves in water to form selenic acid ($\text{H}_2\text{SeO}_4$). The statement is correct.
Step 3: Analyze statement (C): $\text{SeO_2$ is a gas.}
Selenium dioxide ($\text{SeO}_2$) is a white, volatile solid (sublimes at $315^\circ\text{C}$). Its solid structure consists of polymeric chains. Due to its polymeric solid structure, it is not a gas under standard conditions. In contrast, $\text{SO}_2$ is a gas. The statement that $\text{SeO}_2$ is a gas is incorrect.
Step 4: Analyze statement (D): $\text{SO_2$ is a reducing agent.}
Sulfur is in Group 16. In $\text{SO}_2$, the oxidation state of $\text{S}$ is $+4$. $\text{S}$ can be oxidized to $+6$ ($\text{SO}_3$). Since $\text{S}$ can be oxidized, $\text{SO}_2$ typically acts as a strong reducing agent (e.g., $\text{SO}_2 + \text{Cl}_2 \to \text{SO}_2\text{Cl}_2$). The statement is correct.
Step 5: Conclude the final answer.
The incorrect statement is (C).
