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Endeleev saw trends in the physical and chemical properties of elements when he organized them by

Which of the following is a testable hypothesis? a. if i brush my teeth, i will get fewer cavities than if i don't brush my teeth. b. green toothpaste tastes better than blue toothpaste or red toothpaste. c. smart, careful, healthy people always brush their teeth. d. it's wrong to not brush your teeth before you have an important conversation with someone.

If the atomic mass of an atom is 34 and the atom contains 13 protons, how many neutrons does the atom contain?