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

Ex Input:
Passage: All the atoms of a given element have the same number of protons in their nucleus, but they may have different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes . Their nuclei are unstable, so they break down, or decay, and emit radiation. Answer: protons

Ex Output:
All the atoms of a given element have the same number of what in their nucleus, though they may have different numbers of neutrons?

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: Momentum can be calculated by multiplying an object's mass in kilograms (kg) by its velocity in meters per second (m/s). For example, assume that a golf ball has a mass of 0.05 kg. If the ball is traveling at a velocity of 50 m/s, its momentum is:. Answer: momentum

Ex Output:
What can be calculated by multiplying an object's mass in kilograms (kg) by its velocity in meters per second (m/s)?