Zero is the value of water potential of pure water at atmospheric pressure.
1) This is a definition.
2) Protons are given by the bottom number (since atomic number = number of protons).
3) Neutrons = (mass number)-(atomic number), which are the top and bottom numbers, respectively.
4) Nuclear fusion involves combining two things together, which is only reflected by the last option.
5) This is a fact.
6) This is a fact.
7) This is a fact.
8) This is a fact.
9) The correct option is the explanation.
B. Theory
The hypothesis that stand the test of time (often tested and never rejected) is called theory. A theory is supported by a great dealcof evidence.