In order to convert from atoms to moles, we must use Avogadro's number.
Recall that moles are a count. Moles are something like a dozen. If you have a dozen of something, you have twelve of it, regardless of what it is. The same goes for moles. The word "mole" is like the label, the same way the word "dozen" is a label for the number 12. "Mole" means there is Avogadro's number worth of something, or 6.022 * 1023 of something.
If we have 7.50 * 1023 atoms of zinc we can convert it to moles through the ratio 1 mole / 6.022 * 1023.
7.50 *1023 atoms of Zn (1 mol Zn / 6.022 * 1023 atoms of Zn) = 1.25 mol Zn
