I'm not so sure but I would say Answer Choice B
Answer:
The molar mass of the unknown gas is 
Explanation:
Let assume that the gas is O2 gas
O2 gas is to effuse through a porous barrier in time t₁ = 4.98 minutes.
Under the same conditions;
the same number of moles of an unknown gas requires time t₂ = 6.34 minutes to effuse through the same barrier.
From Graham's Law of Diffusion;
Graham's Law of Diffusion states that, at a constant temperature and pressure; the rate of diffusion of a gas is inversely proportional to the square root of its density.
i.e

where K = constant
If we compare the rate o diffusion of two gases;

Since the density of a gas d is proportional to its relative molecular mass M. Then;

Rate is the reciprocal of time ; i.e

Thus; replacing the value of R into the above previous equation;we have:

We can equally say:






The periodic table of elements is divided into columns and rows. The vertical columns represent the groups while the horizontal rows represent the periods. A group of elements usually have similar physical and chemical properties. The first column of the periodic table is made up of 7 elements including SODIUM.
1. The name of the element chosen is sodium and its chemical symbol is Na.
2. Sodium is a metal and thus it has metallic properties.
3. Sodium belongs to group one elements whose family name is ALKALI METALS.
4. The neutral atom of sodium is made up of 11 protons, 11 electrons and 12 neutrons.