Which of the following minerals potentiates the action of insulin?
The total human body contains about 6 mg chromium. The Chromium content of blood is about 20 Mg/dl. Cr performs several biochemical functions such as 
In association with insulin, Cr promotes the utilization of glucose. 
Cr is a component of a protein namely chromodulin which facilitates the binding of insulin to cell receptor sites.
Cr lowers the total serum cholesterol level.
lt is involved in lipoprotein metabolism.
Cr decreases serum low density lipoproteins (LDL) and increases high density lipoproteins (HDL) and, thus, promotes health.
lt is believed that Cr participates in the transport of amino acids into the cells (heart and liver).
It is estimated that an adult man consumes about 10 to 100 mg/day. 
The good sources of Cr include brewer's yeast, grains/ cereals/ cheese and meat.
Chromium deficiency causes disturbances in carbohydrate, lipid and protein metabolisms.
Excessive intake of Cr results in toxicity, leading to liver and kidney damage.

Key Concept:
Chromium in the form of chromodulin facilitates the binding of insulin to cell receptor sites.
Ref : Textbook of Biochemistry, Satyanarayana
Molybdenum
Chromium
Manganese
Selenium