Question

the products of a combustion reaction are usually carbon and water unknown carbon monoxide and hydrogen gas carbon dioxide and water

Explanation:

Combustion reactions typically involve a hydrocarbon reacting with oxygen. In a complete combustion reaction, the products are carbon dioxide ($CO_2$) and water ($H_2O$). For example, the combustion of methane ($CH_4$) is $CH_4 + 2O_2
ightarrow CO_2 + 2H_2O$. Carbon and water are not typical products of a standard combustion reaction (carbon might be a product in incomplete combustion but not usually the main product as stated in the first option). "Unknown" is incorrect as combustion reaction products are well - known. Carbon monoxide and hydrogen gas are not the usual products of a common hydrocarbon combustion (carbon monoxide is a product of incomplete combustion in some cases, but hydrogen gas is not a typical product from the combustion of common organic compounds like hydrocarbons).

Answer:

carbon dioxide and water