$CH_{3}CH_{2}OH$ can be converted into $CH_{3}CHO$ by:

Question

Accepted Answer

$CH_{3}CH_{2}OH$ (ethanol) can be converted into $CH_{3}CHO$ (acetaldehyde) by using pyridinium chlorochromate (PCC). Here is the detailed explanation:

1. **Why Option 3 is Correct:**
   - Pyridinium chlorochromate (PCC) is a mild oxidizing agent that is specifically used to oxidize primary alcohols to aldehydes. In this reaction, PCC oxidizes ethanol ($CH_{3}CH_{2}OH$) to acetaldehyde ($CH_{3}CHO$) without further oxidation to carboxylic acids. This selective oxidation is why PCC is the appropriate reagent for this transformation.

2. **Why the Other Options are Incorrect:**
   - **Option 1: Catalytic hydrogenation**
     - Catalytic hydrogenation is a reduction process, not an oxidation process. It typically involves the addition of hydrogen to unsaturated compounds (like alkenes or alkynes) to form saturated compounds. It would not convert ethanol to acetaldehyde; instead, it would not affect ethanol in the desired way.
   
   - **Option 2: with $LiAlH_{4}$**
     - Lithium aluminum hydride ($LiAlH_{4}$) is a strong reducing agent, not an oxidizing agent. It is used to reduce aldehydes, ketones, and carboxylic acids to alcohols. Using $LiAlH_{4}$ on ethanol would not produce acetaldehyde; instead, it would not change ethanol or could potentially reduce other functional groups if present.
   
   - **Option 4: with $KMnO_{4}$**
     - Potassium permanganate ($KMnO_{4}$) is a strong oxidizing agent that would oxidize ethanol beyond the aldehyde stage to form acetic acid (a carboxylic acid). It is not suitable for stopping at the aldehyde stage, which is required to form acetaldehyde from ethanol.

In conclusion, pyridinium chlorochromate (PCC) is the correct reagent for converting ethanol to acetaldehyde, as it allows for the selective oxidation of primary alcohols to aldehydes without further oxidation to acids.