If you had 15g of O2,how many moles would you have reacting

Can you explain how I'd calculate this please?

Thank you

Simple, the molar mass of oxygen gas is 32.00 grams for every mole of molecules. If you have 15 grams, then you should notice that you have about a half a mole of molecules.

Therefore your answer should be:

M=m/n
n=m/M
n=(15)/(32.00)
n=0.47 mol.

To test yourself further, calculate how many molecules this is.

***Hint: Molecules=moles*Avoogadro's number

To find the number of moles of O2 in 15g, divide by the molar mass.
15g / 32g/mol = .469mol