Which of the following is affected by the concentration of iron in water?

Explanation

Exam-expected option: (4) All of the above.
Dissolved iron unquestionably produces metallic taste and discoloration/staining in water. (U.S. EPA)
The "hardness" part is less cleanly worded: ordinary water hardness is governed mainly by calcium and magnesium, although other multivalent metal ions can contribute. So (4) is probably the intended old-exam answer, but the question is technically loose.