What is the molecular weight of air?

• A. 28g/mol
• B. 29g/mol
• C. 30g/mol
• D. 31g/mol

Answer: (B)

The molecular weight of air is approximately 29 g/mol, which is a value derived from the average composition of air, primarily consisting of nitrogen (approximately 78%) and oxygen (approximately 21%). Nitrogen has a molecular weight of about 28 g/mol, while oxygen has a molecular weight of about 32 g/mol. When calculating the average molecular weight of air, the contributions of these gases in their respective concentrations yield a value close to 29 g/mol.

This average accounts for the mixture of different gases in the atmosphere, making 29 g/mol the most accurate representation of air's molecular weight. The other values, while they represent possible molecular weights for individual components or theoretical mixtures, do not reflect the actual average for the specific composition of atmospheric air.