I would say that descriptive investigations aren't repeatable because it means that you are only describing something - you ask certain question about something, but do not form a hypothesis at that point yet. So it would be a waste of time to simply ask the same questions over and over again with no hypothesis to prove, which is why these types of investigations cannot be repeated.
Answer:
a mutation is a change in a DNA sequence
Explanation:
mutations can result from DNA copying mistakes made during cell division
Nonmetal Atom is the answer.