The correct answer is: D. hydrogen and carbon monoxide.
Synthetic gas, also known as syngas, is a mixture of carbon monoxide and hydrogen. It is produced by the gasification of carbonaceous materials, such as coal, biomass, or natural gas. Syngas can be used as a fuel, as a feedstock for the production of chemicals, or as a precursor for the production of liquid fuels such as synthetic gasoline and diesel.
Option A is incorrect because steam and carbon monoxide do not form a stable mixture. Option B is incorrect because carbon monoxide and nitrogen do not react with each other at high temperatures. Option C is incorrect because hydrogen and methane are not produced by the gasification of carbonaceous materials.