This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Local and Regional Anesthesia, Subject name: Anaesthesia
Pin index system for oxygen 
Select and explain. 
A. 1,5, B. 2,5, C. 4,5, D. 3,5
B: 2,5
Answer: B: 2,5 
Explanation: Ans: (b) 2,5Ref: Miller's Anaesthesia 7th ed. / 675* Pin index for oxygen is 2, 5.* Cylinder of oxygen is black body with white shoulder.GasColor CodePin index positionBodyShoulderOxygenBlackWhite2,5Nitrous oxideBlueBlue3, 5CO2GrayGray1,6HeliumBrownBrown2,5AirGreyWhite/black quartered1,5