Which of the following statement is correct about CO ?

Options

A. It reduces aqueous solution of `PdCl_2` to metallic Pd
B. CO is neutral oxide and acts as a fuel
C. In laboratory it is prepared by dehydrating HCOOH with conc. `H_2SO_4`
D. All are correct

Answer

To determine which statement is correct about carbon monoxide (CO), we will analyze each option provided.

### Step-by-Step Solution:

1. **Analyzing Option A**:
- The statement claims that CO reduces aqueous solution of PdCl2 to metallic palladium (Pd).
- This is true because CO is a reducing agent and can reduce palladium ions in solution to form metallic palladium.
- **Conclusion**: Option A is correct.

2. **Analyzing Option B**:
- The statement claims that CO is a natural oxide and acts as a fuel.
- CO is indeed a natural oxide of carbon and is used as a fuel in various applications, including in combustion processes.
- **Conclusion**: Option B is correct.

3. **Analyzing Option C**:
- The statement claims that in the laboratory, CO is prepared by hydrating HCOH (formaldehyde) with concentrated H2SO4.
- This statement is misleading. CO is actually produced by dehydrating HCOOH (formic acid) with concentrated H2SO4, not by hydrating formaldehyde.
- **Conclusion**: Option C is incorrect.

4. **Analyzing Option D**:
- Option D states that all the previous options (A, B, and C) are correct.
- Since Option C is incorrect, Option D cannot be correct.
- **Conclusion**: Option D is incorrect.

### Final Answer:
- The correct statements about CO are Options A and B. However, since Option C is incorrect, Option D (which states all are correct) is also incorrect.