Question

Name multiple reasons why a cell has a negative charge on the inside.

Answer 1

First, it allows a cell to function as a battery, providing power to operate a variety of "molecular machineries" embedded in the cell membrane.

Second, both the sodium and the potassium ions are positive. Cells (lets take for example neurons) actually have a pretty strong negative charge inside them, whereas there is positive charge outside. This is due to  anions in them which are negatively charged, but are way too big to leave through any channel. They stay put and give the cell a negative charge inside.