Using Graham's Law, it can be calculated that the unknown gas, which effuses 1.66 times faster than CO2, has a molar mass close to that of CH4 (methane), which is 16.04 g/mol.
To calculate the molar mass of the unknown gas using Graham's Law of effusion, you need to understand the law's relation between the rate of effusion and the molar mass of gases. Since the unknown gas effuses 1.66 times more rapidly than CO2, use the formula that expresses Graham's Law: (rate of effusion of gas A / rate of effusion of gas B)2 = (molar mass of gas B / molar mass of gas A).
In this case, the unknown gas (A) is effusing 1.66 times faster than CO2 (B), so: (1/1.66)2 = (Molar Mass of CO2 / Molar Mass of Unknown).
When you plug in the molar mass of CO2 (44.01 g/mol) into the equation and solve for the Molar Mass of the Unknown, it turns out to be close to the molar mass of CH4 (methane), which is about 16.04 g/mol.