Number of atoms : 1.26 x 10²³
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 :
[tex]\tt N=0.21\times 6.02\times 10^{23}\\\\N=1.26\times 10^{23}[/tex]