The intake valve is cooled by:

The intake valve is primarily cooled by the incoming air/fuel mixture as it flows through the intake manifold and into the cylinder. This mixture is at a relatively low temperature compared to combustion gases, which helps to dissipate heat away from the valve itself. As the mixture flows around the valve, it absorbs heat, effectively cooling the valve and preventing it from overheating during operation.

The role of the intake valve is crucial; it opens to allow the air/fuel mixture into the combustion chamber while maintaining a seal during the compression stroke. By being cooled effectively, the valve can maintain its structure and function, enhancing the engine's performance and longevity. The cooling effect is particularly important under high-performance conditions where heat generation is heightened.

In contrast, other options such as exhaust gases typically contribute to heating rather than cooling, engine oil is primarily responsible for lubricating and reducing friction but does not cool the intake valve effectively, and radiation isn't a significant factor in the cooling process of the intake valve in this context. Thus, it's the incoming air/fuel mixture that serves as the proper cooling mechanism for the intake valve.