Final answer:
Potassium (K+) is the principal positively charged ion inside body cells, essential for various cellular functions and maintained by the sodium-potassium pump.
Step-by-step explanation:
The principal positively charged ion inside body cells is potassium (K+). Potassium ions play a crucial role in cell function, including regulating fluid balance and enabling nerve signal transmission and muscle contractions. In the intracellular fluid (ICF), potassium concentrations are maintained at high levels, in contrast to the extracellular fluid (ECF), where sodium (Na+) and chloride (Cl-) ions are more concentrated. This balance in ion concentration is partly regulated by the sodium-potassium pump, which actively transports potassium into the cell and sodium out, using energy from ATP.