Correct Option: (b) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).

Step 1 (Governing Principle): [0.5 Mark]

The solubility of aldehydes and ketones in water is governed by the ability to form hydrogen bonds with water molecules. The general solubility trend is determined by the balance between the hydrophilic carbonyl group ($>C=O$) and the hydrophobic alkyl group ($R-$). As the size of the alkyl group increases, the hydrophobic character dominates, decreasing solubility.

Step 2 (Conceptual Analysis): [0.25 Mark]

• Assertion (A): True. The alkyl group is hydrophobic (water-repelling). As the carbon chain length increases, the non-polar portion of the molecule grows, which hinders the formation of hydrogen bonds with water, thereby decreasing solubility.
• Reason (R): True. Aldehydes and ketones are polar molecules due to the electronegativity difference between carbon and oxygen, resulting in a permanent dipole moment. This leads to dipole-dipole interactions between solute molecules.

Step 3 (Final Conclusion): [0.25 Mark]

While both statements are scientifically accurate, the reason for the decrease in solubility with increasing alkyl chain length is the increase in the hydrophobic effect, not the presence of dipole-dipole interactions. Therefore, (R) is not the correct explanation for (A).

💡 EL10 Concept Insight: Think of the carbonyl group as a "water-loving" anchor and the alkyl group as a "water-hating" tail; as the tail gets longer, it becomes harder for the anchor to pull the whole molecule into the water, regardless of how "sticky" the molecules are to each other.