Question

An unknown gas effuses through an opening at a rate 3.53 times slower than nitrogen gas. What is the molecular mass of the unknown gas?

Answer 1

Pick a number for rate of the unknown gas. Let's say 10 mL/s. Then rate for N2 is 10 x 3.53 = 35.3 mL/s.
[(rate unk gas)/(rate N2)] = sqrt (mm N2/mm unknown)
Substitute and solve for mm (molar mass) unknown gas.
Post your work if you get stuck.