ANS:C - High % of CO in

When fuel undergoes incomplete combustion, it means that it hasn't burned completely due to insufficient oxygen supply or improper combustion conditions. One of the byproducts of incomplete combustion is carbon monoxide (CO). Therefore, a high percentage of carbon monoxide in the exhaust gas is indicative of incomplete combustion. This occurs because carbon monoxide forms when carbon-containing compounds are not completely oxidized to carbon dioxide (CO2). CO is a poisonous gas and a major pollutant, and its presence in exhaust gases suggests that the combustion process has not been efficient.