`A underset("dil"H_(2)SO_(4))overset(K_(2)Cr_(2)O_(7))rarr B underset(H_(2)O)overset(CH_(3)Mgl)rarr (CH_(3))_(3)C-OH`. The reactant A is :

Options

A. `CH_(3)CH(OH)CH_(3)`
B. `CH_(3)COCH_(3)`
C. `C_(2)H_(5)OH`
D. `CH_(3)COOH`

Answer

To solve the question, we need to identify the reactant A based on the given reactions. Let's break down the steps:

### Step 1: Analyze the Reaction
The reaction starts with A being oxidized in the presence of dilute H₂SO₄ and K₂Cr₂O₇. This indicates that A is likely an alcohol, as these reagents are commonly used to oxidize alcohols.

**Hint:** Look for the type of alcohol that can be oxidized to form a ketone or aldehyde.

### Step 2: Determine the Product B
The product B is formed after the oxidation of A. Since the reaction involves K₂Cr₂O₇, which is a strong oxidizing agent, we need to consider what types of alcohols can be oxidized:
- Primary alcohols are oxidized to aldehydes and then to carboxylic acids.
- Secondary alcohols are oxidized to ketones.
- Tertiary alcohols do not oxidize under these conditions.

**Hint:** Identify the type of alcohol that can yield a ketone upon oxidation.

### Step 3: Identify the Grignard Reaction
After the formation of B, the next step involves a Grignard reagent (CH₃MgI) reacting with B. Grignard reagents react with carbonyl compounds (like aldehydes and ketones) to form alcohols.

**Hint:** Determine what type of carbonyl compound would react with a Grignard reagent to yield a tertiary alcohol.

### Step 4: Consider Possible Structures for A
1. **Option 1:** 2-Butanol (CH₃-CH(OH)-CH₂-CH₃)
- Oxidation would yield butan-2-one (a ketone).
- Reaction with CH₃MgI would yield a tertiary alcohol.

2. **Option 2:** Acetone (CH₃-CO-CH₃)
- Oxidation does not apply as it is already a ketone.

3. **Option 3:** Ethanol (C₂H₅OH)
- Oxidation would yield acetaldehyde (an aldehyde), which would then react with CH₃MgI to yield a secondary alcohol.

4. **Option 4:** Methanol (CH₃OH)
- Oxidation would yield formaldehyde, which would react with CH₃MgI to yield a primary alcohol.

**Hint:** Evaluate which of these options can be oxidized to give a ketone that can then react with Grignard reagent to yield a tertiary alcohol.

### Step 5: Conclusion
After analyzing all options, the only suitable reactant A that fits the criteria is **2-Butanol** (Option 1). It can be oxidized to butan-2-one (a ketone) and then react with CH₃MgI to yield a tertiary alcohol.

### Final Answer
The reactant A is **2-Butanol (CH₃-CH(OH)-CH₂-CH₃)**.