An organic liquid `A` containing `C,H` and `O` has a pleasant odour with a boiling point of `78^(@)C`. On boiling. A with conc. `H_(2)SO_(4)` a colourless gas is produced which decolourises bromine water and alkaline `KMnO_(4)`. One mole of this gas also takes one mole of `H_(2)`. The organic liquid `A` is

Options

A. `C_(2)H_(5)Cl`
B. `C_(2)H_(5)CO OCH_3`
C. `C_2H_5 OH`
D. `C_2 H_6`

Explanation

To solve the problem step by step, we will analyze the information given and deduce the identity of the organic liquid `A`.

### Step 1: Analyze the properties of the organic liquid `A`
The organic liquid `A` is described as containing carbon (C), hydrogen (H), and oxygen (O). It has a pleasant odor and a boiling point of 78°C.

**Hint:** Look for common organic compounds with a boiling point around 78°C and a pleasant smell.

### Step 2: Identify potential candidates for `A`
Given the options:
1. C2H5Cl (ethyl chloride)
2. C2H5COOCH3 (ethyl acetate)
3. C2H5OH (ethanol)
4. C2H6 (ethane)

Among these, C2H5OH (ethanol) is known to have a pleasant odor and a boiling point of approximately 78°C.

**Hint:** Ethanol is a common alcohol with a boiling point of 78°C and a characteristic pleasant smell.

### Step 3: Reaction with concentrated H2SO4
When `A` is boiled with concentrated H2SO4, a colorless gas is produced. Concentrated H2SO4 acts as a dehydrating agent, which suggests that `A` must be an alcohol since alcohols can undergo dehydration to form alkenes.

**Hint:** Remember that alcohols can lose water (H2O) when treated with strong acids, leading to the formation of alkenes.

### Step 4: Properties of the gas produced
The colorless gas produced from the reaction with concentrated H2SO4 decolorizes bromine water and alkaline KMnO4. This indicates that the gas is likely an alkene, as alkenes can react with bromine (decolorizing it) and can be oxidized by KMnO4.

**Hint:** The ability to decolorize bromine water is a test for unsaturation (double bonds).

### Step 5: Determine the nature of the gas
The problem states that one mole of the gas takes one mole of H2. This suggests that the gas is a mono-unsaturated compound (an alkene). If it were a di-unsaturated compound (alkyne), it would require two moles of H2.

**Hint:** The stoichiometry of the reaction indicates that the gas is likely an alkene with one double bond.

### Step 6: Conclusion
Since `A` is ethanol (C2H5OH), and upon dehydration with concentrated H2SO4, it produces ethylene (C2H4), which is the colorless gas that decolorizes bromine water and reacts with H2.

Thus, the organic liquid `A` is **C2H5OH (ethanol)**.

**Final Answer:** The organic liquid `A` is C2H5OH (ethanol).