Final answer:
The term for the overall ratio of combustible vapor to air, relative to the stoichiometric ratio that affects post-flashover carbon monoxide levels, is Fuel-to-air ratio.
Step-by-step explanation:
The term for the overall ratio of combustible vapor to air, relative to the stoichiometric ratio that affects post-flashover carbon monoxide levels, is A) Fuel-to-air ratio. This ratio determines the amount of fuel and air needed for optimal combustion. If the fuel-to-air ratio is too high, there may be an excess of fuel, leading to incomplete combustion and higher levels of carbon monoxide.