The mass of one molecule of a substance is 11.79 X 10^-26 kg. What is its molar mass? What could be the substance?

We are given that the mass of one molecule of the substance is 11.79 X 10^-26 Kg. So the mass of one molecule of the substance in grams will be 11.79 X 10^-23 g. The molar mass of a molecule is the mass of 6.023 X 10²³ molecules of that substance. Thus 

mass of 6.023 X 10²³ molecules of the substance = 11.79 X 10^-23 X 6.023 X 10²³

= 71.011 g 

The molar mass of the substance is 71.011 g. This substance could be chlorine gas (Cl₂) as the atomic mass of chlorine is 35.5 and there are two atoms of chlorine per molecule. So molar mass of chlorine molecule = 2 X 35.5 = 71 g