Question

How many moles are 1.20x10^25 formula units of calcium iodide?

Answer 1

Avagadros number states that 1 mol of any substance is made of 6.022 x 10²³ units.

these units could be atoms, molecules or formula units.

therefore 1 mol of Calcium iodide is made of 6.022 x 10²³ formula units

so if 6.022 x 10²³ formula units make up 1 mol

then 1.20 x 10²⁵ formula units - make $\frac{1*1.20*10^{25}}{6.022*10^{23}}$ = 19.9 mol

there are 19.9 mol of CaI₂ present

Answer 2

You should do
1.20x10^25 formula units CaI2 x
1 mol
6.02x10^23
= #### mol