Elements which appear in the same column have similar properties (periodicity). For example, all of the elements in group XVII (17), the Halogens, all react in a similar fashion; they all like to attract one additional electron and form a -1 anion.
C, a compound because it means it was made up of more than one element but, still able to be separated from the other compound(s)
Answer:
12.
1 + 2 + 1 = 4 + 1 + 2 + 1 + 4 = 12 = 4 + 1 + 2 + 1 + 4 = 1 + 2 + 1
Answer:
a scientific procedure undertaken to make a discovery, test a hypothesis, or demonstrate a known fact.
The valence of helium is 0.
