Which is not present in clear hard water

Which of the following chemicals in not present in the clear hard water ?

Which among the following combinations is present in higher amount in hard water?

The degree of hardness of a given sample of hard water is 60 ppm. If the entire hardness is due to MgSO_4, how many of MgSO_4 is present per kilogram of hard water ?

Which of the following is not responsible for hardness of water?

Which of the following is/are hard water (s) ?