1 atom of Al has a mass of?

The mass of 1 mole of Al is 26.98 g.
1 mole of Al contains 6.022 × 10²³ Al atoms.

Mass of one Al atom = (26.98 g) / (6.022 × 10²³) = 4.480 × 10⁻²³ g

It really depends on the isotope.
https://en.wikipedia.org/wiki/Isotopes_of_aluminium

There is one "lighter" unstable version that has a long half life, but is only 0.1% of the aluminum found on Earth. So this will pull down the published mass of "the average aluminum atom" a tiny bit.

Please give "micatkie" Best Answer.