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: Dental
How much is the safely tolerated value of fluoride (mg F/Kg) 
Select and explain. 
A. 4-Feb, B. 8-Apr, C. 16-Aug, D. 32-64
C: 16-Aug
Answer: C: 16-Aug 
Explanation: Certainly lethal dose (CLD) - 32-64 mg F /Kg body weight
Safely tolerated dose (STD) - 8-16 mg F / kg body weight (1/4th of CLD)

Also note these two important values 

Probable toxic dose (PTD)- 2mg F/ Kg body weight
Minimum toxic dose (MTD)- 5-6 mg F/ Kg body weight.