The vapour pressure of an aqueous solution is found to be 750 torr at cetain temperature.'T'. If 'T' is the temperature at which pure water boils under atmospheric pressure and same solution show elevation in boiling point `Delta"T"_("b")=1.04"K",` find the atmopheric pressure `("K"_("b")=0.52"Kg mol"^(-1))`

Options

A. 777
B. 779
C. 782
D. 746

Answer

A

Explanation

`Delta"T"_("b")="K"_("b")xx"Molality"`
`1.04=0.52xx"Molality"`
`"Molality"=2 implies"n"_("solute")=2,"n"_("water")=1000/18`
Now
`("P"^(0)-"P"_("solution"))/"P"_("solution")=("n"_("solute"))/("n"_("water"))`
`("P"^(0)-750)/750=2/55.55`
`"P"^(0)=777" torr"`