Question 2
What does the gradient of the line on a displacement–time graph represent?
The right answer is the one marked above.
The velocity. The gradient is the difference between the y coordinates divided by the difference between the x coordinates. On this graph the y axis carries displacement and the x axis carries time:
gradient = displacement ÷ time = velocity
Acceleration is the gradient of a velocity–time graph, not of a displacement–time graph. Mixing the two up is a common slip — always check what is on the y axis.