Final answer:
The ion with the least total concentration in body fluids is likely potassium (K+), as it is concentrated inside cells and has a much lower presence in the extracellular fluid.
Step-by-step explanation:
In the context of body fluids and their ion concentrations, it is important to consider the various roles that different ions play. The sodium ion (Na+) has the highest concentration in the extracellular fluid (ECF), whereas the potassium ion (K+) is more concentrated inside cells, which is referred to as the intracellular fluid (ICF). It's noted that other ions, such as calcium ion (Ca2+), magnesium ion (Mg2+), and chloride ion (Cl-), also have crucial roles within body fluids. Specifically, chloride helps maintain the electrical neutrality of the ECF by balancing the positive charges of other cations.
Given the background information, the ion with the least total concentration in body fluids is likely one of the cations with significantly lower presence outside of the cells - such as potassium (K+) in the ECF. Potassium is mainly found inside cells and has a much lower concentration in the extracellular fluid, despite its pivotal role within the ICF.