Fluoride is used in
The high energy compound phosphoenol pyruvate is generated from 2-phosphoglycerate by the enzyme enolase. This enzyme requires Mg2+ or Mn2+ and is inhibited by fluoride. For blood  glucose estimation in the laboratory, fluoride is added to the blood to prevent glycolysis by the cells, so that blood glucose is correctly estimated.
Blood glucose estimation samples
Urine glucose estimation samples
Both 1 & 2
None of the above