Final answer:
Vapor lock can occur due to excessive heat near fuel lines or if a fuel line is restricted, with both scenarios leading to an increase in vapor pressure within the fuel system. Option 1 is correct.
Step-by-step explanation:
Vapor lock can occur during both as a result of excessive heat near fuel lines and if a fuel line is restricted. Excessive heat can increase the fuel's temperature leading to higher vapor pressure. If the vapor pressure is too high, fuel can change from a liquid to a gas within the fuel delivery system, preventing the engine from receiving the liquid fuel needed for combustion.
Vapor lock can also happen when a fuel line is restricted. This obstruction can cause heat to build up and induce vapor lock, as the flow of fuel is impeded, elevating the temperature and pressure until vapor lock occurs. Understanding these fundamental principles, such as the fact that the vapor pressure of a liquid increases with temperature according to the ideal gas law (PV=NkBT), helps explain why vapor lock might take place.