Final answer:
To calculate the number of atoms in 30.0 g of K, divide the mass by the molar mass to get the number of moles, then multiply by Avogadro's number.
Step-by-step explanation:
The mass of K is provided, and the corresponding amount of K in moles is requested. Referring to the periodic table, the atomic mass of K is 39.10 amu, and so its molar mass is 39.10 g/mol. The given mass of K (30.0 g) can be divided by its molar mass to calculate the number of moles of K. By using Avogadro's number (6.02 x 10^23), we can then determine the number of atoms in the given mass of K.