\\\\(10^{-3}\\\\) molar \\\\(MgSO_4 = 10^{-3}\\\\) moles of \\\\(MgSO_4\\\\) present in \\\\(1\\\\) Litre.\\\\(n_{CaCO_3} =n_{MgSO_4} \\\\)\\\\(PPM\\\\) (in term of \\\\(CaCO_3) = \\dfrac{10^{-3}\ imes 100}{1000} \ imes 10^6\\\\) \\\\(= 100\\ ppm\\\\)