Below what percentage of oxygen concentration will combustion not be supported?

Combustion is a chemical process that requires sufficient oxygen to occur. Generally, for combustion to happen effectively, the oxygen concentration in the surrounding atmosphere must be above a certain threshold.

In typical atmospheric conditions, oxygen concentration is around 21%. When the concentration falls below approximately 16%, combustion becomes increasingly difficult to sustain, and below 10%, it won't support combustion at all. Specifically, oxygen concentrations below 5% are considered inadequate for ignition or maintaining most types of combustion processes.

Choosing a concentration of 15% as a threshold signifies that while there may still be some ability for combustion to occur at this level, it is not very efficient or reliable. Therefore, combustion would typically not be supported below this level, making it the correct answer regarding effective combustion support.