Explanations:

To calculate the number of atoms in 12.0 g of lithium, we can use the following formula:

Number of atoms = (Mass of substance in grams) / (Atomic mass of substance in grams per mole) x (Avogadro's number)

The atomic mass of lithium is 6.941 g/mol, and Avogadro's number is 6.022 x 10^23 atoms/mol.

Substituting the given values into the formula, we get:

Number of atoms = (12.0 g) / (6.941 g/mol) x (6.022 x 10^23 atoms/mol)

Number of atoms ≈ 4.14 x 10^23 atoms

Therefore, there are approximately 4.14 x 10^23 atoms of lithium in 12.0 g of lithium.