Hard water contains relatively large concentrations of A. Magnesium ions
B. Calcium ions
C. Iron ions
D. All of these ions

D.

All of these ions

Explanation:

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I think the answer is All of these ions

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.

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