Gas cylinder with single pin index -

Ans. is 'd' i.e., Entonox GasPin indexOxygen2,5Nitrous oxide3,5Cyclopropane3,6Air1,5Nitrogen1,4Entonox (50% O2 + 50% N2O)Single central (7)Carbon dioxide (< 7[?]5%)2,6Carbon dioxide (>7[?]5%)1,6