The reagent(s) used for softening the temporary hardness of water is (are):

C a_{3} (P O_{4})_{2}

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C a (O H)_{2}

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N a_{2} C O_{3}

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N a O C l

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Solution

The correct options are
B $C a (O H)_{2}$
C $N a_{2} C O_{3}$
D $N a O C l$
The reason for temporary hardness is owing to the presence of bicarbonates of Ca and Mg.
To remove this temporary hardness, we have to use agents that can precipitate out the
bicarbonates in an easy-to-filter-out form:

$C a (H C O_{3})_{2} + N a_{2} C O_{3} ⟶ C a C O_{3} ↓ + N a H C O_{3}$

$C a (H C O_{3})_{2} + C a (O H)_{2} ⟶ 2 C a C O_{3} ↓ + 2 H_{2} O$

The hypochlorite anion is oxidizing and gets hydrolyzed to $^{-} O H$ .

$O C l^{-} (a q) + H_{2} O (l) ⇌ H O C l (a q) +^{-} O H (a q)$

Calcium phosphate is just insoluble in water. It is useful in this context.

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Temporary hardness can be removed by mixing water with slaked lime, this process is known as softening of water.

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