If gold number of A, B, C and D are 0.005, 0.05, 0.5 and 5 respectively, then which of the following will have the greatest protective value? 

• Protective power is inversely proportional to gold number. Gold number with highest value will have low protective power, whereas gold number with lowest value will have high protective power 
• Gold number A have low value, this implies that it has highest protective power. 

Hence the correct option is (A).