Asample of he gas (2.0 mmol) effused through a pinhole in 53 s. the same amount of an unknown gas, under the same conditions, effused through the pinhole in 248 s. the molecular mass of the unknown gas is g/mol.

Molecular mass of unknown gas is 87.58 grams per mol.

Explanation:

Let x be the molecular mass of the unknown gas.

Rate of effusion of a gas and its molecular mass is related as:

r ∝

where r is rate and M is molecular mass.

Molecular mass of He gas = 4 g/mol

Given: Same amount of gas is effused and at same conditions.

Let us say V mL of gas effused.

Then rate = V/t where t is time taken for effusion.

Since same amount of gases are effused V doesn't matter.

We can say:

t ∝ √M ⇒

then

Hence molecular mass of unknown gas is 87.58 grams per mol.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.