Which of the following numerical expressions gives the number of moles in a sample containing mass m (in grams) of a substance with molar mass M (in g/mol)?

• A. m + M
• B. M / m
• C. m / M
• D. m × M

Answer: (C)

Verified step by step guidance

1. Recall the definition of a mole: it is a unit that measures the amount of substance, specifically the number of particles (atoms, molecules, etc.).
2. Understand that the molar mass \(M\) (in grams per mole) tells us how many grams correspond to one mole of the substance.
3. To find the number of moles \(n\) in a sample, you divide the mass of the sample \(m\) (in grams) by the molar mass \(M\) (in grams per mole). This is because the molar mass acts as a conversion factor between grams and moles.
4. Write the formula for the number of moles as: \(n = \frac{m}{M}\).
5. Evaluate the given options by comparing them to the formula \(n = \frac{m}{M}\) to identify the correct expression.