Correct Option
The Assertion states that synthetic detergents can lather well in hard water. This statement is true. Hard water contains high concentrations of dissolved calcium (Ca²⁺) and magnesium (Mg²²⁺) ions. Unlike conventional soaps, which react with these ions to form insoluble precipitates (scum), synthetic detergents are designed to function effectively in such conditions. They do not form scum, thus maintaining their lathering and cleaning efficiency.
The Reason states that synthetic detergents form soluble calcium and magnesium salts with hard water. This statement is also true. The chemical composition of synthetic detergents enables them to interact with Ca²⁺ and Mg²⁺ ions present in hard water to produce compounds that remain dissolved in the water. These soluble compounds do not precipitate out or interfere with the detergent's ability to form lather.
The Reason provides a correct explanation for the Assertion. The fundamental reason why synthetic detergents can lather effectively in hard water (Assertion) is precisely because they form soluble salts with the hardness-causing ions (Reason), thereby preventing the formation of insoluble scum. Therefore, both the Assertion and the Reason are true, and the Reason is the correct explanation for the Assertion.
Incorrect Options
Options 2, 3, and 4 are incorrect. Option 2 is incorrect because the Reason does provide a correct explanation for the Assertion. Options 3 and 4 are incorrect because both the Assertion and the Reason are factually true statements.