What is the charge of an ion that has 12 protons and 13 electrons

Each proton serves as a positive charge and each electron serves as a negative charge. The two charges neutralize each other on a 1:1 ratio. In your question, you have 12 protons to 13 electrons. That means there's a net -1 charge because there is one more electron than protons.

Nonmetals usually react by gaining electrons