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MCQ practice · SSC Chemistry Board questions · Chapter 9: Acid-Base Balance

Sylhet Board 2021

Which is the formula of lime water?

Think it through first, then pick an option.

  1. a CaCO₃
  2. b CaO
  3. c Ca(OH)₂
  4. d Ca(HCO₃)₂
Answer and explanation

Correct answer: c Ca(OH)₂

The book writes lime water as Ca(OH)₂: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

Why the other options are wrong

  • a CaCO₃: CaCO₃ is limestone, not lime water; lime water is a Ca(OH)₂ solution.
  • b CaO: CaO is lime; its solution in water is lime water, Ca(OH)₂.
  • d Ca(HCO₃)₂: Ca(HCO₃)₂ forms with excess CO₂; lime water is Ca(OH)₂.