The correct answer to the question is option 1: accelerated.

When the passenger tosses the coin upward, it falls behind him. This suggests that the train is accelerating.

To understand why this is the case, we need to consider the effects of acceleration on objects inside the train. In this scenario, when the train accelerates, there is a force acting on both the passenger and the coin in the same direction as the acceleration.

When the passenger tosses the coin upward, it initially moves with the same velocity as the train. However, as the coin moves upward, it experiences a downward force due to gravity. The combination of the downward force of gravity and the acceleration of the train causes the coin to fall behind the passenger.

If the train were moving with a uniform velocity or along a circular track, the coin would not fall behind the passenger.

Therefore, option 1, accelerated, is the correct answer.