Calculate the mass (in grams) of cobalt that has the same number of atoms as 521 mg of silicon.

The atomic mass of silicon is 28 g/mol.

Therefore, 521 mg or 0.521 g will be equivalent to;

0.521/28 = 0.01861 mooles

Atomic mass of cobalt is 27 g/mol

According to Avogadro's law the mass of cobalt that will have the same atom as 52 mg of silicon will be;

(0.01861 moles * 27) = 0.5024 g or 502.4 mg