Multiple choice

Water, on passing over the rocks, becomes hard because it dissolves

  1. calcium carbonate

  2. sodium chloride

  3. sodium carbonate

  4. sodium phosphate

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Water becomes hard as it flows over rocks because it dissolves minerals, specifically calcium and magnesium carbonates or sulfates. Calcium carbonate is the most common contributor to temporary hardness.