Which among path length and displacement cannot be zero for a moving object?

Which of the following is a one-dimensional motion?

Under what condition is the magnitude of distance covered by an object equal to its displacement?

$A$ person travels $10\, km$ north and $20\, km$ east. What will be the displacement from the initial point in $km$?

The magnitude of the displacement is equal to the distance covered in a given interval of time if the particle

In which of the following examples of motion can the body be considered approximately a point object:
$(a)$ $A$ railway carriage moving without jerks between two stations.
$(b)$ $A$ monkey sitting on top of a man cycling smoothly on a circular track.
$(c)$ $A$ spinning cricket ball that turns sharply on hitting the ground.
$(d)$ $A$ tumbling beaker that has slipped off the edge of a table.