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Directions: For the Assertion (A) and Reason (R) given below, choose the correct alternative. Assertion (A): Clothes are not washed properly in hard water. Reason (R): Hard water contains many dissolved minerals.

Difficulty: Easy

Correct Answer: Both A and R are true and R is the correct explanation of A.

Explanation:


Introduction / Context:

This Assertion–Reason question tests understanding of the everyday problem of washing clothes in hard water and connects it to the underlying chemistry. Many competitive exams include such applied science questions because they relate textbook concepts like hardness of water, dissolved salts and soap action to real-life situations.


Given Data / Assumptions:

  • Assertion (A): Clothes are not washed properly in hard water.
  • Reason (R): Hard water contains many minerals.
  • We must judge whether A and R are individually true and whether R correctly explains A.
  • Hardness of water is mainly due to dissolved calcium and magnesium salts.


Concept / Approach:

Hard water is water that contains significant concentrations of dissolved calcium and magnesium ions. When soap is used in hard water, these ions react with the soap to form an insoluble scum instead of lather, making it difficult to clean clothes. The Reason mentions “many minerals” in hard water, which is a simpler way of referring to these dissolved salts. We must see whether this is an accurate and sufficient cause for the washing problem described in the Assertion.


Step-by-Step Solution:

Step 1: Evaluate Assertion (A). It is well known that soap does not lather easily with hard water and washing efficiency is reduced, so clothes are not cleaned properly. Thus A is true. Step 2: Evaluate Reason (R). Hard water indeed contains a high concentration of dissolved mineral salts, especially of calcium and magnesium. So R is also true in a general sense. Step 3: Link R to A. The extra dissolved mineral ions react with soap molecules to form insoluble precipitates (often called “scum”) instead of allowing soap to create stable lather. Step 4: Because less effective lather is formed, the soap cannot remove dirt and grease efficiently from fabric surfaces. The net result is that clothes remain partially dirty even after washing. Step 5: Therefore, the presence of many dissolved minerals in hard water is the underlying reason for clothes not being washed properly. R directly and correctly explains A.


Verification / Alternative check:

We can compare washing with hard water and soft water. In soft water, which has very low concentrations of calcium and magnesium ions, soap quickly forms lather and cleaning is efficient. Adding calcium or magnesium salts to the same water immediately reduces lather and produces scum, reproducing the behaviour of hard water. This experimental observation supports R as the cause of A.


Why Other Options Are Wrong:

Choosing “both A and R are true but R is NOT the correct explanation” would be wrong because the presence of mineral ions is exactly what interferes with washing.

Options where A is true but R is false, or A is false while R is true, contradict well-established facts about hardness of water and laundering.


Common Pitfalls:

Some students think “many minerals” is too vague and dismiss R, but in the exam context it is a simplified way of saying that dissolved calcium and magnesium salts are present. Others forget that soaps behave differently from synthetic detergents, which are often designed to work better in hard water. The question is specifically about soap-based washing in hard water.


Final Answer:

The correct option is Both A and R are true and R is the correct explanation of A.

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