Which of the following is NOT a factor in determining the rate of combustion?

The rate of combustion is influenced by several key factors, and the color of the flame produced is not one of them. The color of the flame can provide some information about the combustion process, such as indicating the efficiency of combustion or the presence of certain elements, but it does not directly influence how quickly the combustion occurs.

The type of fuel used is critical, as different fuels have varying chemical compositions and energy content, which directly affect the combustion rate. Similarly, the quality of the air supplied is essential because adequate oxygen levels are necessary for efficient combustion; insufficient or contaminated air can slow the process down. The temperature of the environment plays a role as well, since higher temperatures can enhance the combustion rate by facilitating the chemical reactions involved.

Therefore, while flame color may be an interesting observation, it does not directly impact the dynamics of how quickly a substance burns, making it the correct choice for the option that is NOT a factor in determining the rate of combustion.