If a train is slowing down it is accelerating

1. True. Acceleration can be in any direction. If the velocity and acceleration are in opposite directions the object is slowing down which is the case here.  

2. True. With the distance traveled per unit time you can calculate the velocity over each interval and by analyzing the changes in velocity find values of acceleration over time intervals. 

3. False. An object moving in circular motion is subjected to a constant centripetal force directed towards the center of the circle. Though the speed is not changing, the direction of the motion is changing since velocity is a vector and thus the acceleration affects the direction. 

4. False. Average acceleration is the change in speed divided by the time interval over which it occurs. The change in speed here is 100 km/h and it occurs over 2 hours and thus the average acceleration is 50 km/h^2.

No if a train is slowing down than the trains speed is slowing down instead of increasing