O2 Pin-Index 2-5 — FRCA Primary MCQ
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Correct answer: B — 2 and 5
Pin-index positions: O2 = 2-5 / N2O = 3-5 / Air = 1-5 / CO2 = 2-6 / Entonox = 7. The Bodok seal (a neoprene washer) between the cylinder valve and the yoke ensures a gas-tight connection. The pin-index system prevents incorrect cylinder-yoke connections.
Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment