Question

Consider the following statements and select the correct option: Statement-I : Solubility of aliphatic amines in water decreases with increase in molecular mass. Statement-II : On increase in size of the hydrophobic alkyl part, higher amines become insoluble in water.

• A. Both Statement-I and Statement-II are correct and Statement-II justifies Statement-I.
• B. Both Statement-I and Statement-II are incorrect.
• C. Statement-I is correct but Statement-II is incorrect.
• D. Statement-I is incorrect but Statement-II is correct.

Hint:

Solubility trend of aliphatic amines in water: \[ \text{Methylamine} \gt \text{Ethylamine} \gt \text{Propylamine} \gt \text{Butylamine} \] Increasing alkyl chain length increases hydrophobic character and decreases solubility.

Answer 1

The Correct Option is A

Step 1: Think about how amines dissolve.
Small amines dissolve in water because the $N-H$ part and the lone pair on nitrogen form hydrogen bonds with water.

Step 2: Check Statement-I.
As the molecular mass of an aliphatic amine rises, the carbon chain gets longer, and solubility in water drops. So Statement-I is correct.

Step 3: Check Statement-II.
The reason is that the bigger alkyl (hydrophobic) part dislikes water more and more, so higher amines become insoluble. So Statement-II is correct.

Step 4: See if II explains I.
Statement-II gives exactly the reason behind Statement-I, the growing water-hating alkyl part is why solubility falls. So II is a correct explanation of I.

Step 5: Match to the options.
Both statements are correct and II justifies I, which is the first option.

Step 6: State the answer.
\[ \boxed{\text{Both correct; Statement-II justifies Statement-I}} \]