Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

[EX Q]: Question: As a polycrystalline material solidifies, grains with irregular shapes form. the interfaces between grains constitute grain what? Answer: boundaries
[EX A]: Grain boundaries. As a polycrystalline material solidifies, grains with irregular shapes form. The interfaces between grains constitute grain boundaries. (Squares represent unit cells within grains.

[EX Q]: Question: Electrons in the "outer shell" are also known as what kind of electrons? Answer: valence
[EX A]: Determine the total number of valence (outer shell) electrons. For cations, subtract one electron for each.

[EX Q]: Question: Frequency and intensity are two measurable properties of what? Answer: wave
[EX A]:
All waves can be defined in terms of their frequency and intensity.