Select the incorrect statement(s):

Options

A. In `K_(2)MnO_(4)` and `CrO_(2)Cl_(2)` the central transition metals/ions have same oxidation state.
B. Both sodium and potassium dichromate can be used as primary standard in volumetric estimations.
C. Potassium dichromate on strong heating evolves oxygen gas and forms green powder.
D. Potassium dichromate on strong heating evolves oxygen gas forms green powder and black powder

Explanation

To solve the question, we need to evaluate each statement regarding K2MnO4 and CrO2Cl2, sodium and potassium dichromate, and the products formed when potassium dichromate is heated. Let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement 1: In K2MnO4 and CrO2Cl2, the central transition metals have the same oxidation state.**
- For K2MnO4:
- Let the oxidation state of Mn be \( x \).
- The oxidation states of K and O are +1 and -2, respectively.
- The equation can be set up as:
\[ 2(+1) + 4(-2) + x = 0 \implies 2 - 8 + x = 0 \implies x = +6 \]
- For CrO2Cl2:
- Let the oxidation state of Cr be \( x \).
- The oxidation states of O and Cl are -2 and -1, respectively.
- The equation can be set up as:
\[ 2(-2) + 2(-1) + x = 0 \implies -4 - 2 + x = 0 \implies x = +6 \]
- Both Mn and Cr have an oxidation state of +6.
- **Conclusion:** This statement is correct.

2. **Statement 2: Sodium and potassium dichromate can be used as primary standards in volumetric estimations.**
- Potassium dichromate (K2Cr2O7) is a primary standard due to its stability and known composition.
- Sodium dichromate (Na2Cr2O7) is less stable and can absorb moisture, making it unsuitable as a primary standard.
- **Conclusion:** This statement is incorrect.

3. **Statement 3: Potassium dichromate on strong heating evolves oxygen gas and forms a green powder.**
- When K2Cr2O7 is heated, it decomposes to form K2CrO4, which is green, and CrO3, along with the evolution of oxygen gas.
- The reaction can be summarized as:
\[ 2 K2Cr2O7 \rightarrow 2 K2CrO4 + 2 CrO3 + O2 \]
- The green powder formed is K2CrO4.
- **Conclusion:** This statement is correct.

4. **Statement 4: Potassium dichromate on strong heating evolves oxygen gas, forms green powder, and black powder.**
- As established, K2Cr2O7 decomposes to form K2CrO4 (green powder) and CrO3, but does not produce a black powder.
- Therefore, the mention of a black powder is incorrect.
- **Conclusion:** This statement is incorrect.

### Final Evaluation:
- The incorrect statements are **Statement 2** and **Statement 4**.

### Answer:
The correct option will be **Statement 2 and Statement 4**.