Question

`25mL` samples of distiled water, tap water and boiled water required, respectively, `1mL, 13mL` and `5mL` of soap solution to form a permanent lather. The ratio of temporary to permanent hardness in the tap water is
A. `3:2`
B. `2:3`
C. `1:2`
D. `2:1`

Answer 1

Correct Answer - D
Volume soap solution used effectively in tap water
`=13-1=12mL`
`therefore` Teporary`+` permanent hardness `=12mL`
Volume of soap solution used effectively in boiled water `=5-1=4mL`
permanent hardness`=4mL`
`therefore` Temporary`+` Permanent hardness`=12mL`
Permanent hardness`=4mL`
Temporary hardness`=8mL`
`therefore("Temporary hardness")/("Permanent hardness")=(8)/(4)=2:1`