Which of the following statement(s) is(are) incorrect ?

Options

A. In thioure test for nitric ,a green coloured solution is obtained
B. it is not necessary to carry out the chromyl chloride test in a dry test tube
C. In `PbNO_(3)` the brown ring test can be performed with its water extract
D. Suspension of `CdCO_(4)` gives black ppt , with sodium sulphide solution

Explanation

To determine which statements are incorrect from the given options, we will analyze each statement one by one based on the knowledge of qualitative inorganic salt analysis.

### Step-by-Step Solution:

1. **Analyze Option A:**
- **Statement:** "In thorium test for nitrite, a green colored solution is obtained."
- **Analysis:** The thorium test for nitrite actually produces a deep red coloration due to the formation of Fe-S-C-N-Al(III). Therefore, the statement claiming a green color is incorrect.
- **Conclusion:** Option A is incorrect.

2. **Analyze Option B:**
- **Statement:** "It is not necessary to carry out the chromyl chloride test in a dry test tube."
- **Analysis:** The chromyl chloride test must be performed in a dry test tube because the presence of moisture can lead to the formation of H2CrO4 and HCl, which would interfere with the test. Thus, the statement is incorrect.
- **Conclusion:** Option B is incorrect.

3. **Analyze Option C:**
- **Statement:** "In lead nitrate, a brown ring test can be performed with its water extract; a white precipitate of lead sulfate is formed, and hence the brown ring is not visible."
- **Analysis:** The brown ring test involves the formation of a complex with iron and nitrate ions. If a white precipitate of lead sulfate forms, it can indeed hinder the visibility of the brown ring. Thus, this statement is also incorrect.
- **Conclusion:** Option C is incorrect.

4. **Analyze Option D:**
- **Statement:** "Suspension of cadmium CO3 gives a black precipitate with sodium sulfide solution."
- **Analysis:** Cadmium carbonate (CdCO3) actually gives a yellow precipitate of cadmium sulfide (CdS) when reacted with sodium sulfide (Na2S), not a black precipitate. Therefore, this statement is incorrect.
- **Conclusion:** Option D is incorrect.

### Final Conclusion:
All options A, B, C, and D are incorrect.