A solution containing 3.3 g of a substance in 125g of benzene `(b.p 80^(@)C)` boils at `80.66^(@)C.` If `K_(b)` for one litre of benzene is `3.28^(@)C,` the molecular mass of the substance shall be

Options

A. 127.2
B. 131.2
C. 137.12
D. 142.72

Answer

B

Explanation

`Delta T_(b) = (K_(b) xx W_(2))/(M_(2) xx W_(1))=1000` `:. M_(2) = (1000K_(b) W_(2))/(W_(1) Delta T_(b))=(1000 xx 3.28 xx 3.3)/(125 xx 0.66)=131.2`