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# A sample of hard water contains 68ppm of $CaSO_4$,then the hardness of the same sample of water is

$\begin{array}{1 1}(a)\;68\\(b)\;100\\(c)\;200\\(d)\;50\end{array}$

68ppm means 68 parts of $CaSO_4$ in 1 million ,136ppm $CaSO_4\Rightarrow 100$degree
Hardness of the same sample of water is 50
Hence (d) is the correct answer.