I believe the answer is C.
Answer:
19. 1, 2, 3, 4, 5, 6, 7, 8
20. Li=1+, Be=2+, B=3+, C=4+
21. N=3-, O=2-, F=1-
Explanation:
Well you know that you have to balance out the equation to 0. So if I is -1 and Ca is +2 you know that I had to equal to -2. So you can do that by having two of them. So Ca=+2 and I2=-2 so CaI2 would equal 0 meaning that would be the correct answer. Hope that I explained that correct :)
They should probably wear gloves. A pH of 2.0 is a very strong acid, and it can easily irritate their hands. They should also remember to NEVER touch their face, mouth, etc. and to keep all chemicals on the laboratory table.
