Given a scientific passage and an answer, generate a question for the given answer.
--------
Question: Passage: Some nonmetals are very reactive, whereas others are not reactive at all. It depends on the number of electrons in their outer energy level. Answer: reactivity

Answer: The number of electrons in the outer energy level determines what property of nonmetals?

Question: Passage: The strength of bases is measured on a scale called the pH scale, which ranges from 0 to 14. On this scale, a pH value of 7 indicates a neutral solution, and a pH value greater than 7 indicates a basic solution. The higher the pH value is, the stronger the base. The strongest bases, such as drain cleaner, have a pH value close to 14. Answer: ph scale

Answer: The strength of bases is measured on what scale?

Question: Passage: The weight of an object is the force pulling the object downward. On Earth, this would be the gravitational force of the Earth on the object. On the moon, this would be the gravitational force of the moon on the object. The gravitational force of the moon is one-sixth the magnitude of the gravitational force of the Earth; the weight of the moon rock on the moon will be one-sixth the weight of the moon rock on the Earth's surface. Weight is measured in force unitsnewtonsby a calibrated spring scale as shown here. Answer: weight

Answer:
What is the force pulling an object downward called?