Which of the following would cause an atom to have a positive electric charge? a. having more protons than electrons b. having more electrons than protons c. having more electrons than neutrons d. having more neutrons than protons and electrons

In neutral state the atom got an equal number of protons (+) and electrons (-). If you lose and electron then you will have 1 more proton than electron, so you have a +, but if you gained an electron, then you'd have one more electron than protons, so you'd get a -. 
Fx: carbon has 6 protons and 6 electrons. If carbon loses an electron, then the carbon atom would have 6 protons and only 5 electrons, then you'd have 6+ and 5-, which is 1 more plus and minuses, so you have C+. 
If Carbon gained an electron, then you'd have 6+ and 7-, which is 1 more minus than pluses, so you'd have C-. 
Last example, if you gained 2 electrons, then you'd have 6+ and 8-, which is 2 more minuses than pluses, which would give you an C-- (Also known as: C2-)