Given a scientific passage and an answer, generate a question for the given answer.

Ex Input:
Passage: The Universe contains about a hundred billion galaxies. Answer: about a hundred billion

Ex Output:
Approximately how many galaxies are there in the universe?

Ex Input:
Passage: By losing an electron, the sodium atom becomes a sodium ion. It now has one less electron than protons, giving it a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na + . Answer: becomes sodium ion

Ex Output:
What happens when a sodium atom loses an electron?

Ex Input:
Passage: Diffusion can occur across a semipermeable membrane, such as the cell membrane, as long as a concentration gradient exists. Molecules will continue to flow in this manner until equilibrium is reached. At equilibrium, there is no longer an area of high concentration or low concentration, and molecules flow equally in both directions across the semipermeable membrane. At equilibrium, equal amounts of a molecule are entering and leaving a cell. Answer: concentration gradient

Ex Output:
Diffusion can occur across a semipermeable membrane, such as the cell membrane, as long as a what exists?