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The hardness of a water sample (in terms of equivalents of CaCO 3 ) containing 10 –3 M CaSO 4 is (Molar mass of CaSO 4 = 136 g mol –1 )

1. 90 ppm
2. 100 ppm
3. 50 ppm
4. 10 ppm

Correct answer: 100 ppm

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