Assertion (A) >: Soaps do not form lather with water containing salts of calcium and magnesium. Reason (R) >: Calcium and magnesium salts of long-chain fatty acids are insoluble in water.

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Q: 91 (CDS-I/2009)

Assertion (A): Soaps do not form lather with water containing salts of calcium and magnesium.
Reason (R): Calcium and magnesium salts of long-chain fatty acids are insoluble in water.

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,27,16,27,6,6,4

keywords: 

{'soaps': [0, 0, 1, 2], 'lather': [0, 0, 0, 1], 'magnesium salts': [0, 0, 2, 1], 'fatty acids': [0, 0, 1, 0], 'salts': [0, 0, 2, 0], 'calcium': [2, 0, 0, 4], 'magnesium': [1, 0, 2, 3], 'water': [65, 15, 80, 129]}

Option 1 states that both the assertion and the reason are true, and the reason correctly explains why the assertion is true.

The assertion (A) states that soaps do not form lather with water containing salts of calcium and magnesium, which is true. When soaps come into contact with hard water, which contains these salts, they react with the calcium and magnesium ions to form insoluble compounds. These compounds are not easily dissolved in water and therefore, do not produce lather.

The reason (R) states that calcium and magnesium salts of long-chain fatty acids are insoluble in water, which is also true. Soaps are made up of long-chain fatty acids, and when these fatty acids react with calcium and magnesium ions in hard water, they form insoluble compounds that cannot dissolve in water. As a result, lather formation is hindered.

Therefore, in this case, the reason correctly explains why the assertion is true. So, option 1 is the correct answer.