CHEMISTRY // Which of the following gases SUPPRESSES combustion?

A gas can suppress combustion if
(1) the gas must not be flammable and must not support combustion; and
(2) the gas must be denser than air so that it can cover the flame.

a) is false
Hydrogen is flammable.

b) is true
Carbon dioxide is not flammable and does not support combustion. Also, it is denser than air so that it can cover the flame.

c) is false
Although carbon dioxide is not flammable and does not support combustion, it is less slightly dense that air so that it cannot cover the flame.

d) is false
Oxygen supports combustion.

The answer: b) Carbon Dioxide

The answer they are looking for is b) Carbon Dioxide.
Nitrogen would work as long as it displaces enough oxygen.