Stable elements are those that are unlikely to react with other elements, and unstable are those that are highly reactive. Stable elements are the noble gases (full outer shell - won't bond with others). The unstable elements should be the ones in Group 1 and Group 7 because they bond together easily since they have a "desire" to fill their outer shell.
I think the correct answer from the choices listed above is option D. Simple diffusion is the cell transport that allows small molecules to move from an area of higher concentration to an area of lower concentration without energy being <span>required from the cell.</span>
