How many calcium atoms are in 31.2 g of calcium?

To find the number of atoms in calcium one has to multiply a given mole of Calcium by Avogadro's number since each mole of a substance contains 6.03 * 10²³.

Now, mol of Ca = mass of Ca : molar mass of Ca

mol of Ca = 31.2 g : 40 g/mol

mol of Ca = 0.78 mol

⇒ atoms of Ca = 0.78 mol * (6.02 * 10²³ atoms/mole)

= 4.696 * 10²³ atoms