How many atoms of Ca are present in 80.156 grams of Ca?

1.2044 x 10²⁴ atoms.

Explanation:

We need to calculate the no. of moles of Ca that are present in 80.156 g using the relation:

n = mass/atomic mass = (80.156 g) / (40.078 g/mol) = 2.0 mol.

It is known that every 1.0 mole of a molecule contains Avogadro's number of molecules (NA = 6.022 x 10²³).

Using cross multiplication:

1.0 mole of Ca contains → 6.022 x 10²³ atoms.

2.0 moles of Ca contains →? atoms.

∴ 2.0 mole of (80.156 g) Ca contain = (2.0 mol) (6.022 x 10²³) = 1.2044 x 10²⁴ atoms.