Question

You have 0.21 moles of Al how many atoms do you have

Answer 1

Number of atoms : 1.26 x 10²³

Further explanation  

The mole is the number of particles(molecules, atoms, ions) contained in a substance  

1 mol = 6.02.10²³ particles

Can be formulated

N=n x No

N = number of particles

n = mol

No = Avogadro's = 6.02.10²³

0.21 moles of Al, so n = 0.21

Number of atoms :

$\tt N=0.21\times 6.02\times 10^{23}\\\\N=1.26\times 10^{23}$