A) \[Mg{{(HC{{O}_{3}})}_{2}},\] temporary hardness, washing soda method
B) \[CaC{{O}_{3}},\] temporary hardness, boiling method
C) \[MgS{{O}_{4}},\] permanent hardness, calgon's method
D) \[CaC{{I}_{2}},\] permanent hardness, Clark's method
Correct Answer: C
Solution :
Temporary hardness is because of the presence of bicarbonates of \[M{{g}^{2+}}\] and \[C{{a}^{2+}}\]. The methods used for their removal are: (1) boiling method (2) dark's method, \[Ca{{(HC{{O}_{3}})}_{2}}+Ca{{(OH)}_{2}}\to \]\[2CaC{{O}_{3}}+2{{H}_{2}}O\] Permanent hardness is because of the presence of \[SO_{4}^{2-}\], \[C{{l}^{-}}\] etc of \[M{{g}^{2+}}\] and \[C{{a}^{2+}}\]. The methods used for their removal are: (1) Washing soda method, \[MC{{l}_{2}}+N{{a}_{2}}C{{O}_{3}}\to \]\[MC{{O}_{3}}+2NaCl\] (2) Calgon's method \[{{M}^{+}}+\]\[N{{a}_{4}}{{P}_{6}}{{O}^{2-}}_{18}\to \,N{{a}_{2}}M{{P}_{6}}\,{{O}^{2-}}_{18}\]
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