Which gas is proposed to be released directly from a solid to gas in the outgassing model?

• A. Hydrogen
• B. Nitrogen or Carbon Monoxide
• C. Oxygen
• D. Neon

Answer: (B)

In the outgassing model, gases escape from solids mainly through sublimation: a direct solid-to-gas transition as temperature or pressure changes, without passing through a liquid phase. Nitrogen and carbon monoxide are both extremely volatile in solid form, so their ices readily sublimate at the low temperatures typical of the environments being modeled. That makes them likely to be released directly from solid to gas, aligning with the idea of outgassed volatiles appearing without melting first.

Hydrogen can sublimate, but in many solids it’s bound up in minerals or molecules rather than existing as a free, easily sublimating ice. Oxygen is less volatile under the same conditions, and neon is a noble gas that isn’t typically trapped in solids in a way that would cause direct solid-to-gas release in this context.