question_answer 55)

  Which of the following ions will cause hardness in water sample? (a) \[C{{a}^{2+}}\]                           (b) \[N{{a}^{+}}\]                             (c) \[C{{l}^{-}}\]                                 (d) \[{{K}^{+}}\]

Answer:

  (a) \[C{{a}^{++}}\]ions in the form of \[Ca{{(HC{{O}_{3}})}_{2}}\]or \[CaC{{l}_{2}}\]or\[CaS{{O}_{4}}\] cause hardness in water, i.e., soluble salts of calcium can cause hardness in water.