Incomplete combustion of fuel produces:
(A) CO2
(B) CO
(C) H2O
(D) H2

To determine the products of incomplete combustion of fuel, let's analyze the options provided:

Incomplete Combustion: This occurs when there is not enough oxygen to allow the fuel to react completely. The main characteristics of incomplete combustion include the production of carbon monoxide (CO) and other hydrocarbons, rather than the complete products like carbon dioxide (CO2) and water (H2O).

Common Products of Incomplete Combustion:

Carbon Dioxide (CO2): This is produced during complete combustion when there is sufficient oxygen.
Carbon Monoxide (CO): This is a primary product of incomplete combustion. It forms when carbon in the fuel is not fully oxidized due to limited oxygen supply.
Water (H2O): This is also produced during complete combustion but can occur in smaller amounts during incomplete combustion.
Hydrogen (H2): This is not typically a product of combustion reactions; instead, it's usually a reactant in chemical reactions or can be produced in other processes like electrolysis.
Now, let’s evaluate the options:

(A) CO2 - This is produced during complete combustion, not incomplete.

(B) CO - This is produced during incomplete combustion due to the lack of sufficient oxygen.

(C) H2O - This is typically produced during complete combustion, although small amounts may be produced during incomplete combustion.

(D) H2 - This is not a typical product of combustion processes.

Conclusion: The correct answer is (B) CO. Incomplete combustion of fuel primarily produces carbon monoxide (CO) due to insufficient oxygen.