UPSC Prelims 2002·GS1·science-and-technology·materials and robotics

Assertion (A): Synthetic detergents can lather well in hard water. Reason (R): Synthetic detergents form soluble calcium and magnesium salts with hard water.

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  1. ABoth A and R are individually true and R is the correct explanation of ACorrect
  2. BBoth A and R are individually true but R is not a correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Explanation

The correct answer is A because both the assertion and the reason are scientifically accurate and directly related. Hard water contains calcium and magnesium ions. When ordinary soap is used in hard water, it reacts with these ions to form insoluble precipitates known as scum, which prevents lathering. In contrast, synthetic detergents are designed to remain effective in hard water. The Reason provided is correct because the calcium and magnesium salts formed by synthetic detergents are soluble in water. Since these salts do not precipitate out as scum, the detergent molecules remain free to foam and clean, allowing them to lather well. Therefore, the reason perfectly explains why the assertion is true.
science-and-technology: Assertion (A): Synthetic detergents can lather well in hard water. Reason (R): Synthetic detergents form soluble calcium
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