Answer:
The number of atoms in the outermost shell
Explanation:
For example, the electron shells in the alkali metals contain the following numbers of electrons:
Li: 2, 1
Na: 2, 8, 1
K: 2, 8, 8, 1
They all have one electron in their outermost shell, and they have similar chemical properties.
Density = Mass / Volume
Density = 2.74g / 3.10cm³
Density = 0.88 g/cm³
The answer to the question above is 3