You will find that the atomic weight of oxygen is about 16. Since the weight of the protons and neutrons is about 1 (the electrons weigh almost nothing compared to protons and neutrons) and we know we have 8 protons in the nucleus, we can calculate the number of neutrons by subtracting 8 from 16 (16 - 8) which equals 8.
The answer is "A. a pure substance can be separated by chemical means, while a mixture can be separated by physical means". A pure substance only has one type of substance, whereas a mixture has more than one. A pure substance therefore, can only be separated chemically, because it is not two things mixed together, whereas a mixture can be separated physically because there are multiple substances.
1. D
2. A
3. B
4. C
5. E
6. I
7. J
8. L
9. M
10. G
11. H
12. K
13. F
