How many times more massive is a copper atom than an aluminum atom?

2.355 times

Explanation: An aluminium atom has an atomic mass of 26.98 g while a copper atom has an atomic mass of 63.55 g. The ratio of the mass of Aluminium atom to mass of a copper atom is:

= 26.98 g : 63.55 g

= 1 : 2.355

Therefore, the mass of a copper atom is 2.355 times the mass of an aluminium atom. A copper atom is 2.355 times more massive than an aluminium atom.