Here's how to calculate the number of atoms in 4.2 moles of aluminum:

1. Avogadro's Number

* Avogadro's number tells us the number of particles (atoms, molecules, etc.) in one mole of a substance. It's approximately 6.022 x 10^23 particles/mole.

2. Calculation

* Step 1: Multiply the number of moles by Avogadro's number:

4.2 moles Al * (6.022 x 10^23 atoms/mole) = 2.53 x 10^24 atoms

Therefore, there are approximately 2.53 x 10^24 atoms in 4.2 moles of aluminum.