Determine the number of atoms in 2.50 mol zn

For 1 mole of any substance, there are 6.02214086 × 10^23 particles (atoms, molecules, ions, etc. depending on the substance). This number is called Avogadro's Constant

So, for 1 mole of water, there are 6.02214086 × 10^23 water particles, and so on.

So in 2.5 moles of Zinc, you multiply Avogadro's Constant by 2.5 (the number of moles). In doing this you get the 1.0554 × 10^24