How many moles are in 15.0 grams of calcium?
0.374 moles
2.67 moles
601.5 moles
2.40 x 1025 moles

Use the atomic mass of calcium

Ca atomic mass = 40.1 g / mol

Now use the formula:

 mass = #moles * atomic mass, and solve for #moles

#moles = mass / atomic mass = 15.0g / 40.1g/mol = 0.374 mol

0.374 moles