What do hydrogen and oxygen molecules have in common?

Hydrogen and oxygen molecules share a common trait in terms of size despite their differences in structure and properties. Both hydrogen (H₂) and oxygen (O₂) are diatomic molecules, meaning they consist of two atoms bonded together. However, hydrogen is the smallest molecule among the elements, while oxygen is larger.

The criterion of size in this context can refer to their molecular size relative to each other, as both are gases at room temperature and share a similar state of matter. This commonality contrasts with other attributes; for instance, their charge differs significantly, given that both are neutral molecules but with different behaviors in reactions. Reactivity varies widely, with hydrogen being much more reactive compared to oxygen under specific conditions. Density plays a role as well, but hydrogen is less dense than oxygen, further illustrating that size in its relative characteristics is their shared aspect. Thus, in the comparison, size is the appropriate choice to highlight a common feature of hydrogen and oxygen molecules.