MCQ practice · SSC Chemistry Board questions · Chapter 9: Acid-Base Balance
Which compound causes permanent hardness of water?
Think it through first, then pick an option.
- a MgSO₄
- b K₂SO₄
- c Na₂SO₄
- d ZnSO₄
Answer and explanation
Correct answer: a MgSO₄
MgSO₄ is a magnesium sulfate, which causes permanent hardness.
Why the other options are wrong
- b K₂SO₄: K₂SO₄ has no Ca, Mg or Fe, so it causes no hardness.
- c Na₂SO₄: Na₂SO₄ has none of the hardness metals (Ca, Mg, Fe).
- d ZnSO₄: The book does not name zinc as a hardness metal.
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