SI unit of length - meters
Answer: The best reason the scientific community will accept a theory is if it is proven.
The answer is Al.
If it is a main group element with 3 electrons in its Lewis dot structure, it must be in group 3A. If it is in the 3p orbital section, then it must be in period 3, since the p orbital is a valence orbital and the number that preceeds it is the principal quantum number. Therefore, your answer is the element in period 3 and group 3A, which is aluminum.
Mixtures are made up of 2 or more substances that are together in the same place but aren’t chemically bonded.