Which of the following is prohibited when riding a freight car?

Riding on the end platform of a tank car is prohibited because this area poses significant safety risks. The end platform is generally narrow and can be unstable, increasing the likelihood of losing balance or being thrown off the car during movement. Safety protocols prioritize maintaining secure and stable positions while on freight equipment, and the design of tank cars, along with their operation, makes end platforms particularly hazardous.

In contrast, maintaining three-point contact is essential for safety when riding freight cars, as it helps ensure stability and reduces the risk of falling. Riding with feet firmly placed is also encouraged for the same reasons. Riding on the outer edge, while also a concern due to potential instability, does not inherently relate to a specific prohibition like riding on the end platform does. Hence, those practices are acceptable compared to the dangers posed by the end platform of a tank car.