Hi Kathy,
I'll put my scientist hat on here...
The electrolytes we are concerned about as biological creatures are sodium (Na+) and Potassium (K+). They have lots of roles in our bodies from helping with nervous system transmissions, to making sure the right stuff gets into and out of our cells. The plus (+) means that by themselves they are positively charged (which is what allows them to do their job) but cannot exist alone so they need a negatively charged partner. Thus Chlorine (Cl-) and Phosphate (PO4-) come alone for the ride. There are other counter ions that can work, nitrate, acetate, citrate etc. and you sometimes see in mineral formulations, but these are the cheapest to purify from Mother Nature. Chlorine has a few minor jobs in the body. But phosphate is a biggie, so neither go to waste.

OK, lesson over... and no exam to follow :p

Chlorine? I thought that I had read, 'Chloride.'

Sorry for the confusion. Chloride is the ion (Cl-). Chlorine (Cl) is the element as you would find in the periodic table. I do not know why those chemists insist on making the naming convensions to very confusing - try looking at all the names for the different forms of iron (Fe) :eek:.