If at certain temperature, the vapour pressure of pure water is 25 mm Hg and that of a very dilute aqueous urea solution is 24.5 mm Hg, the molality of the solution is

Options

A. `0.02`
B. `1.2`
C. `1.11`
D. `0.08`

Answer

C

Explanation

`(P^(@)-P_(s))/(P^(@))=(w_(B))/(m_(B))xx(m_(A))/(w_(A)), (w_(B))/(w_(B)xx w_(A))xx1000xx(m)/(1000)`
`rArr (P^(@)-P_(s))/(P^(@))=" molality " xx(m)/(1000)`
`(25-24.5)/(25)=m xx(18)/(1000)`
`m=(0.02xx1000)/(18)=1.11`