Click on the reset button. Expand the Net Charge' and 'Mass Number' menus by clicking the green + on the right side of the boxes. Change the numbers of protons, neutrons, and electrons and observe the effects of these changes on the net charge and mass number of the element. Answer the following questions after you've Investigated what happens. 15. What variables are you manipulating in this exercise? Identify a symbol to represent each variable.​