Calculate the number of atoms in 0.9g of Al.

To calculate the number of atoms in 0.9g of Al, we first need to determine the molar mass of aluminum (Al), which is approximately 26.98 g/mol.

Next, we need to convert the mass of Al from grams to moles using the formula:

moles = mass / molar mass

moles = 0.9g / 26.98 g/mol
moles = 0.03336 mol

Finally, we can calculate the number of atoms in 0.9g of Al using Avogadro's number, which is approximately 6.022 x 10^23 atoms/mol:

number of atoms = moles x Avogadro's number
number of atoms = 0.03336 mol x 6.022 x 10^23 atoms/mol
number of atoms = 2.01 x 10^22 atoms

Therefore, there are approximately 2.01 x 10^22 atoms in 0.9g of Al.