Why do compact fuels burn more slowly than less compact fuels?

The correct reasoning lies in the fact that compact fuels have a more tightly packed structure, which restricts the flow of oxygen and heat around the fuel particles. The combustion process relies on the availability of both oxygen and heat to sustain the fire. In compact fuels, the densification can create limited surface area for reactions, making it challenging for oxygen to penetrate and interact with the fuel. This reduced circulation means that the combustion process will be less efficient, causing these fuels to burn more slowly compared to less compact fuels, where airflow and heat can circulate more freely.

While other choices may touch on different aspects of combustion, they do not accurately address the dynamics between compactness and the accessibility of oxygen and heat, which are critical factors in the rate of burning.