This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition and health, Subject name: Social & Preventive Medicine
All are trace elements except - 
Select and explain. 
A. Iron, B. Fluoride, C. Potassium, D. Zinc
C: Potassium
Answer: C: Potassium 
Explanation: Trace elements are elements required by the body in quantities of less than a few milligrams per day.eg.iron,iodine,flourine,zinc,copper cobalt,chromium,manganese,molybdenum,selenium,nickel,tin,silicon and vanadium.(Ref.PARK'S textbbok of sociala and preventive medicine 21st edition page no.573)