Which of the following statements is /are incorrect?

Options

A. A filter paper moistened with cadmium acetate solution turn yellow, when brought in contact with `H_(2)S` gas.
B. Both carbonate ions as well as bicarbonate ions in the solutions, give reddish-brown precipitate with mercury `(II)` chloride.
C. Sulphites in presence of zinc, reacts with dilute `H_(2)SO_(4)` to liberate `SO_(3)` gas.
D. A filter paper moistened with `KIO_(3)` and starch turns blue in contact with `SO_(2)` vapours.

Explanation

To determine which statements are incorrect, we will analyze each statement one by one based on the provided information.

### Step-by-Step Solution:

1. **Statement A**: "A filter paper moistened with cadmium acetate solution turned yellow when brought in contact with H2S gas."
- **Analysis**: When cadmium acetate reacts with H2S gas, it forms cadmium sulfide (CdS), which is yellow in color. Therefore, this statement is **correct**.

2. **Statement B**: "Both carbonate ion as well as bicarbonate ions in solution give reddish brown PPT with mercuric 2 chloride."
- **Analysis**: The carbonate ion (CO3^2-) reacts with mercuric chloride (HgCl2) to form a reddish-brown precipitate (Hg2CO3). However, bicarbonate ions (HCO3^-) do not form a precipitate with mercuric chloride. Therefore, this statement is **incorrect**.

3. **Statement C**: "Sulfites in presence of zinc reacts with diluted H2SO4 to liberate SO3 gas."
- **Analysis**: When sulfites (SO3^2-) react with zinc in the presence of diluted H2SO4, they produce hydrogen sulfide (H2S) gas, not sulfur trioxide (SO3). Therefore, this statement is **incorrect**.

4. **Statement D**: "A filter paper moistened with KI O3 and starch turns blue in contact with SO2 vapors."
- **Analysis**: The reaction between SO2 and potassium iodate (KIO3) in the presence of starch does indeed produce a blue color due to the formation of iodine. Therefore, this statement is **correct**.

### Conclusion:
The incorrect statements are **B and C**.