D. because matter is uniform through and cannot be separated into other substances by physical means.
Atomic Mass is equal to the sum of the number of protons and neutrons.
Thus the atomic mass = 3 + 4
= 7
Answer: 1. Block
2. True ( I'm unsure. He arranged it according to mass, but he is credited for the periodic table)
3. Noble gasses
4. technetium
5. Alkaline earth metals
6. Number of protons
7. False
8. Not true: generally decreases as atomic number increases within a period
9. Argon
10. Four
11. False
12. False
Explanation:
