If molality of pure gas A is `(100)/(1.2)` then calculate its molar mass.

Options

A. `120 gm//"mol"`
B. `100 gm//"mol"`
C. `12 gm//"mol"`
D. can not be determined

Answer

C

Explanation

Molality of pur gas `A = (100)/(1.2)`
Molality `= ("Moles of solute")/("Mass of solvent in gm") xx 1000`
`= ("Mass of solute in gram")/(MM xx "Mass of solvent in gram") xx 1000`
In case of pure substance, solute and solvent are same
`(100)/(1.2) = (1000)/(MM)`
`MM = 12 gm//mol`