Unknown compound (A) `C_(5)H_(10)O` give positive test with `2,4` - DNP
but negative test with Tollen's reagent. It also give yellow precipitate with `I_(2)//NaOH` . (A) is :

Options

A.
B.
C.
D.

Explanation

To identify the unknown compound (A) with the molecular formula \( C_5H_{10}O \), we will analyze the information given in the question step by step.

### Step 1: Analyze the 2,4-DNP Test
The compound gives a positive test with 2,4-Dinitrophenylhydrazine (2,4-DNP), indicating that it contains a carbonyl group (C=O). This means that compound (A) could be either an aldehyde or a ketone.

**Hint:** 2,4-DNP test is used to identify carbonyl compounds, which can be either aldehydes or ketones.

### Step 2: Analyze the Tollens' Reagent Test
The compound gives a negative test with Tollens' reagent. Tollens' reagent is used to differentiate between aldehydes and ketones. Aldehydes will reduce Tollens' reagent and produce a silver mirror, while ketones do not react. Since (A) gives a negative test, we can conclude that (A) is a ketone.

**Hint:** A negative result with Tollens' reagent indicates that the compound is not an aldehyde, thus it must be a ketone.

### Step 3: Analyze the Iodine Test with NaOH
The compound also gives a yellow precipitate with iodine in the presence of sodium hydroxide (NaOH). This indicates that (A) undergoes the iodoform reaction, which is characteristic of methyl ketones (ketones with the structure \( RCOCH_3 \)) or compounds that can be converted into such structures.

**Hint:** The iodoform reaction is indicative of the presence of a methyl ketone or a compound that can form a methyl ketone.

### Step 4: Determine the Structure of Compound (A)
Given that (A) is a ketone and gives a positive iodoform reaction, we can deduce that it must be a methyl ketone. The molecular formula \( C_5H_{10}O \) suggests that the structure could be 3-pentanone or 2-butanone. However, only 3-pentanone fits the criteria of being a methyl ketone.

**Hint:** Look for a structure that fits the molecular formula and has a methyl group adjacent to the carbonyl group.

### Conclusion
Based on the above analysis, the unknown compound (A) is **3-pentanone**.

**Final Answer:** Compound (A) is 3-pentanone.