There are two water samples one in test-tube A and another in test-tube B. It was observed that water in both test-tubes A and B does not give lather with soap. However, after boiling the water in both the test-tubes A and B, the water in test-tube B does give lather with soap. Which among the following statements is correct?

Water in both the test-tubes is permanent hard water

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Water in test-tube A is permanent hard water while in test-tube B is temporary hard water

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Water in test-tube A is temporary hard water while in test-tube B is permanent hard water

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Water in both the test-tubes is temporary hard water

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Solution

The correct option is B Water in test-tube A is permanent hard water while in test-tube B is temporary hard water
The water in both test-tubes A and B does not give lather with soap. Hard water doesn't form lather and contains impurities like hydrogen carbonate, sulphates or chlorides of calcium and magnesium. So water in both the test-tubes is hard.

Also, it is given that after boiling, water in test-tube B does give lather with soap. So, water in test-tube B has temporary hardness while that in A has permanent hardness.

Soft water contains low concentrations of calcium and magnesium ions. It forms lather easily with soap and is suitable for use.

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