To solve our problem we have to convert the molecules into moles and then we have to convert the moles into grams.
One mol is similar to a dozen. When we want a dozen eggs we mean that we need 12 eggs. When we want a mol of eggs we mean that we need 6.022 * 10^23 eggs. So a mol of something is 6.022 * 10^23 of that.
1 mol of molecules = 6.022 * 10^23 molecules
We can use that relationship to find the number of moles of calcium iodide that we have in 1.20 * 10^25 molecules of it.
moles of CaI₂ = 1.20 * 10^25 molecules * 1 mol/(6.022*10^23 molecules)
moles of CaI₂ = 19.9 moles
Now we can convert those moles of CaI₂ into grams using the molar mass of it.
atomic mass of Ca = 40.08 amu
atomic mass of I = 126.90 amu
molar mass of CaI₂ = 40.08 + 126.90 * 2
molar mass of CaI₂ = 293.88 g/mol
mass of CaI₂ = moles of CaI₂ * molar mass of CaI₂
mass of CaI₂ = 19.9 moles * 293.88 g/mol
mass of CaI₂ = 5848 g
Answer: if we round it to 3 SF we get 5850 g.