17. (3pts) Most of calcium in nature exists as 40Ca2+, but there is a measurable amount of isotopes with mass number of 42,43 and 44 . Write the nuclear symbol (just one) that represents a mixture of these isotopes. 18. (9pts) Consider the subatomic particles a. Which contribute most to its mass? b. Which contribute most to its charge? c. Which take up the most space? 19. (2pts) Describe the difference between the terms "atomic number" and "mass number