This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Forensic Medicine
While dispatching blood and urine for chemical analysis, sodium fluoride is added as preservative in the following concentration - 
Select and explain. 
A. 30 mg/10 ml, B. 40 mg/10 ml, C. 50 mg/ ml, D. 100 mg/10 ml
D: 100 mg/10 ml
Answer: D: 100 mg/10 ml 
Explanation: 10 mg/ml of Na-fluride (i.e. 100 mg/10 ml) is used with 3 mg of potassium oxalate for preserving blood.