Carbon monoxide can occur in:

The correct answer is: All of these

The correct option is d)All of these.

• CO is not added to tobacco, but is produced when tobacco is incompletely burned. This happens when there isn't enough oxygen to convert all the carbon in cigarettes to harmless carbon dioxide. Cigarette smoke can contain large amounts of CO. Water pipes are also an important source of CO exposure.
• Incomplete combustion of fuel produces the toxic gas carbon dioxide/carbon monoxide. Incomplete combustion of fuel produces the toxic gas carbon dioxide/carbon monoxide.
• 99% of the gas molecules released in volcanic eruptions are water vapor (H2O), carbon dioxide (CO2) and sulfur dioxide (SO2). The remaining 1% consists of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other trace gases.