JEE Main General: States of Matter questions with solutions

Q1. One mole of nitrogen gas at a pressure of 0.8 atm takes 38 s to effuse through a small pinhole. Under the same conditions but at a pressure of 1.6 atm, one mole of a xenon fluoride compound takes 57 s to effuse through the same hole. What is the molar mass (in g/mol) of the xenon fluoride compound?

1. 128
2. 196
3. 254
4. 320

Answer: 254

Using the modified Graham's law where effusion rate is proportional to P/sqrt(M), setting the rates equal for both gases gives the molar mass of the xenon fluoride as 254 g/mol, which corresponds to XeF4.