Crossed Cannizzaro reaction can be given by following combination:

Options

A. `CH_(3)`CHO, HCHO
B. `C_(6) H_(5)`CHO,`CH_(3)`CHO
C. `C_(6) H_(5)`CHO, HCHO
D. All of these

Explanation

To determine which combination can undergo a crossed Cannizzaro reaction, we need to consider the following criteria:

1. **Presence of Two Different Aldehydes or Ketones**: The reaction requires two different carbonyl compounds.
2. **Alpha Hydrogen Equals Zero**: At least one of the carbonyl compounds must not have any alpha hydrogens (i.e., the carbon adjacent to the carbonyl carbon must not have any hydrogens).

Now, let's evaluate the provided options step by step:

### Step 1: Analyze Option A
- **Combination**: CH3CHO (acetaldehyde) and HCHO (formaldehyde).
- **Alpha Hydrogen Check**:
- CH3CHO has 3 alpha hydrogens (from the CH3 group).
- HCHO has 0 alpha hydrogens.
- **Conclusion**: Since one of the compounds has alpha hydrogens, this combination cannot undergo a crossed Cannizzaro reaction. **Option A is incorrect.**

### Step 2: Analyze Option B
- **Combination**: CH3CHO (acetaldehyde) and another CH3CHO (acetaldehyde).
- **Alpha Hydrogen Check**:
- CH3CHO has 3 alpha hydrogens.
- **Conclusion**: Both compounds are the same and have alpha hydrogens. This combination cannot undergo a crossed Cannizzaro reaction. **Option B is incorrect.**

### Step 3: Analyze Option C
- **Combination**: C6H5CHO (benzaldehyde) and HCHO (formaldehyde).
- **Alpha Hydrogen Check**:
- C6H5CHO has 0 alpha hydrogens (the carbon adjacent to the carbonyl is part of a phenyl ring).
- HCHO has 0 alpha hydrogens.
- **Conclusion**: Both compounds are different, and at least one (benzaldehyde) has zero alpha hydrogens. This combination can undergo a crossed Cannizzaro reaction. **Option C is correct.**

### Step 4: Analyze Option D
- **Combination**: CH3COCH3 (acetone) and CH3CHO (acetaldehyde).
- **Alpha Hydrogen Check**:
- CH3COCH3 has 6 alpha hydrogens (from the two CH3 groups).
- CH3CHO has 3 alpha hydrogens.
- **Conclusion**: Both compounds have alpha hydrogens. This combination cannot undergo a crossed Cannizzaro reaction. **Option D is incorrect.**

### Final Answer:
The correct combination that can undergo a crossed Cannizzaro reaction is **Option C: C6H5CHO and HCHO**.

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