Several centimeters of lead. Gamma rays have the highest penetrating power and therefore need a thick layer of something, in most cases lead, to prevent penetration. (This is why if you have ever go to the dentist they put a heavy thing on you made of lead, to prevent the penetration of gamma rays that can destroy your most important organs).
16. A
17. B
18. B
19. B
20. A
21. B
22. A
23. D
24. C
25. D
26. A
27. B
Combustion reaction
Key: O2
O2 is normally in a chemical formula when you are used to burn anything, so basically, anything with O2 involves burning.
