Katrina Nathan, age 11, of Peoria, I11., for her question:

HOW IS POTASSIUM IMPORTANT TO HUMANS?

Potassium is a silvery metallic element. Humans must have it since it plays a part in the process by which organisms change food into energy and new tissue. If a person's diet includes fruit, vegetables and meat, he will be supplied with enough potassium for normal body needs.

Potassium is also the lightest metal except lithium. It is so soft that it can be cut with a knife. The metal and its compounds make up nearly two and a half percent of the earth's crust.

Some potassium alloys are used in the heat transfer systems of nuclear reactors. They use potassium carbonate, also called potash, in making certain types of glass and soap. Potassium nitrate is used in producing matches and explosives while other compounds are used for medical purposes and even commercial fertilizers.