The atomic number of carbon is 6. How many electrons does an ion of carbon have if it is represented by the symbol shown below? 12C1-

The answer is 7 electrons. We know that Carbon has 6 electrons, so we could see that there is the charge that is - 1, meaning there has to be one more electron than proton because that means it's gained an electron of - 1 charge. Therefore 7 electrons to 6 protons.