What common feature do hydrogen and oxygen molecules share?

Hydrogen and oxygen molecules share the common feature of having the same charge on each electron, which is negative. In elemental hydrogen, each atom has one electron, while in elemental oxygen, each atom has eight electrons. Regardless of the number, all electrons possess the same fundamental charge, which is approximately -1.6 x 10^-19 coulombs. This uniformity in charge is a key characteristic of all electrons across different atoms, including those of hydrogen and oxygen.

The other options represent different concepts that do not apply equally to both hydrogen and oxygen. For instance, both hydrogen and oxygen have different numbers of protons (hydrogen has one, and oxygen has eight) and varying numbers of neutrons. Additionally, the number of atoms does not apply since molecules can consist of multiple atoms; thus, it does not serve as a common feature between the two elements. The uniqueness of the electron charge firmly establishes why that is the correct answer.