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The domestic water supply is treated by bleaching powder to remove unhygienic species in water and to make it safe for drinking water. However, this given rise to `Ca^(2+)` and `Cl^(-)` ion contamination in water. Both these ions are also injurious for health if a minimum concentration is crossed. The chloride ions are tested by a kit provided by many companies having `AgNO_(3)` solution that is added drop by drop to `23 mL` of water sample to which an indicator has been added. When sufficient silver nitrate is added to remove `Cl^(-1)` ions as `AgCl` solid, the solid turns orange. The colour change is noticed by addition of `AgNO_(3)` having molar concentration such that each drop `(0.05 mL)` of `AgNO_(3)` converts `12.5 mg` of `Cl^(-)` ions `AgCl`.
Assuming that concentration of `Ca^(2+)` ions in solution is equal equivalence ratio to chloride ions, the hardness of water is:
A. `9.185xx10^(3)"ppm"`
B. `6.185xx10^(3)"ppm"`
C. `1.185xx10^(3)"ppm"`
D. `4.185xx10^(3)"ppm"`

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Correct Answer - A
Eq. of `CaCO_(3)="Eq.of" Ca^(2+)= "Eq.of" Cl^(-)`
( for `1 "litre"` water)
`(w)/(100//2)=0.1837`
`w_(CaCO_(3))=(0.1837xx100)/(2)=9.185 g`
`therefore` Hardness =`(9.185xx10^(6))/(10^(3))`
`9.185xx10^(3)"ppm"`

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