I need the answer with the number if it is a, b, c or d because it is an obj

The number of moles of a substance is a measure of the amount of that substance. It is directly related to the mass of the substance and its molar mass.

The formula to calculate the number of moles ($n$) is the mass ($m$) of the substance divided by its molar mass ($M$).

A. Moles = Mass / Molar Mass
B. Moles = Molar Mass / Mass
C. Moles = Mass x Molar Mass
D. Moles = Volume / Molar Mass

Option A correctly represents the formula for calculating the number of moles.

The final answer is $\boxed{\text{A}}$.