Achemist dissolves 0.400 mol benzene in 800 grams of substance x, then finds the boiling point of substance x has increased by 1.4°c. what is the
molal boiling point elevation constant (kb) for substance x?
a) 3.2°c/m
b) 0.70°c/m
c) 2.8°c/m
d) 1.40cm

Explanation:

The  molal boiling point elevation constant (Kb) of a substance is defined as change in boiling point / its molality.

For substance X, the change in boiling point = 1.4°C

Its molality = 0.4 mol / 800 g = 0.4 mol / 0.8 kg = 0.5 m

So Kb = 1.4 / 0.5 = 2.8°C/m

The answer is C).

it's filtration, but this is an assumption so my apologies if i got this