Answer:
1.25*10^24 atoms with sig figs
Step-by-step explanation:
To find the number of atoms, an easy way to do this would be to convert the mass to the number of moles, then convert moles to the number of atoms.
There are 40.08 grams of calcium per mole, so 83.4 grams of calcium would have 83.4/40.08 moles of calcium, or about 2.081 moles of calcium
Each mole of something contains about 6.022*10^23 of that something, so 2.081 moles of calcium atoms would equal 2.081 *(6.022*10^23) atoms. 2.081 *(6.022*10^23) equals 1.25*10^24, so there would be 1.25 * 10^24 atoms in 83.4 grams of calcium