PASSAGE-IV : A neutral organic compound A of molecular formula `C_(2)H_(6)O`, on oxidation with potassium dichromate and sulphuric acid gives an acidic compound B. The compound A reacts with B on warming in presence of conc. `H_(2)SO_(4)` to give a sweet smelling substance C. C on heating with D gives back A.
Identify the reagent D.

Options

A. `H_(2)O`
B. `NaOH`
C. Conc. `H_(2)SO_(4)`
D. `K_(2)Cr_(2)O_(7)`

Explanation

To solve the problem, we need to identify the organic compounds and the reagents involved in the reactions described. Let's break it down step by step.

### Step 1: Identify Compound A
The molecular formula for compound A is given as \( C_2H_6O \). This formula corresponds to ethanol, which is an alcohol.

**Hint:** Look for common organic compounds that match the given molecular formula.

### Step 2: Oxidation of Compound A
When ethanol (compound A) is oxidized using potassium dichromate (\( K_2Cr_2O_7 \)) and sulfuric acid (\( H_2SO_4 \)), it is converted into an acidic compound. The product of this oxidation is ethanoic acid (acetic acid), which is compound B.

**Hint:** Remember that alcohols can be oxidized to form acids.

### Step 3: Reaction of A with B
Now, compound A (ethanol) reacts with compound B (ethanoic acid) in the presence of concentrated sulfuric acid (\( H_2SO_4 \)). This reaction is known as esterification, where an ester is formed. The product of this reaction is a sweet-smelling substance, which we can identify as ethyl acetate (compound C).

**Hint:** Esterification involves the reaction of an alcohol with an acid to form an ester and water.

### Step 4: Heating Compound C with Reagent D
The problem states that compound C (ethyl acetate) is heated with another reagent D to regenerate compound A (ethanol). The reagent D that can achieve this is sodium hydroxide (\( NaOH \)), which can hydrolyze the ester back into the alcohol and acid.

**Hint:** Think about hydrolysis reactions that can reverse ester formation.

### Conclusion
The reagent D that regenerates compound A (ethanol) from compound C (ethyl acetate) is sodium hydroxide (\( NaOH \)).

### Final Answer
The reagent D is \( NaOH \).

### Summary of Steps:
1. Identify compound A as ethanol (\( C_2H_6O \)).
2. Oxidize ethanol to form ethanoic acid (compound B).
3. React ethanol with ethanoic acid to form ethyl acetate (compound C).
4. Use sodium hydroxide (D) to hydrolyze ethyl acetate back to ethanol.