Various tests while conducting a fuel oil analysis can be performed on board to facilitate proper centrifugation. What test provides the key data for selecting the correct purifier gravity disk for fuel oil centrifugal purifiers?

Correct Answer: Option D — Density

Density is the critical factor for selecting the correct gravity disk in a centrifugal purifier. The gravity disk must be sized based on the fuel's density to establish the correct interface position within the bowl, ensuring efficient separation of water and contaminants from the fuel oil during the purification process.