From the periodic table:
mass of Br = 79.9 grams
mass of Ar = 39.9 grams
Therefore,
molar mass of Ar = 39.9 grams
molar mass of Br2 = 2(79.9) = 159.8 grams
Now,
time for Ar / time for Br2 = sqrt(molar mass of Ar / molar mass of Br2)
time for Ar = 48 * sqrt(39.9 / 158.9)
time for Ar = 24.0528 minutes
