Question

The vapour pressure of acetone at 20°C is 185 torr. When 1.2 g of a non-volatile substance was dissolved in 100 g of acetone at 20°C, its vapour pressure was 183 torr. The molar mass (g mol^-1) of the substance is

(a) 32 (b) 64 (c) 128 (d) 488

Comments

Relative lowering vapour pressure formula is
P°-P/P°
But you are saying P°-P/P
I'm confused where to apply what ?

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P°-P/P° is used for volatile substance.

Answer 1

Correct option (b) 64 

Explanation: