Final answer:
The flash point is the temperature at which fuel vapor can ignite, and diesel has a higher flash point than gasoline, making it the safer choice for use onboard vessels due to lower volatility and reduced risk of accidental ignition.
Step-by-step explanation:
The term flash point is the temperature at which fuel vapor can ignite in the presence of an ignition source. It is a key indicator of the flammability and handling safety of a combustible liquid. In comparing gasoline and diesel, diesel has a higher flash point, making it less volatile and safer in terms of ignition under normal conditions. Consequently, diesel is preferred for vessels primarily due to safety considerations; its higher flash point means it is less likely to combust accidentally.
The correct answer to the question is: (c) Flash point is the temperature at which fuel vapor can ignite. Diesel has a higher flash point. Diesel is preferred for vessels due to safety.