Final answer:
Negative acceleration, or deceleration, is represented by a train coming to a halt because it signifies a decrease in speed over time. Other cases such as a car starting from rest, a stone falling, or a bus moving at a constant speed do not describe deceleration.
Step-by-step explanation:
The case that represents a negative acceleration is when a train is coming to a halt. This is because the term 'negative acceleration', otherwise known as deceleration, refers to a decrease in speed over time. Thus, when a train slows down until it stops, it is undergoing negative acceleration. This is unlike cases where a car is starting from rest (which describes positive acceleration), or a bus moving at a uniform velocity (which means zero acceleration), or a stone falling from a height (which also represents positive acceleration due to gravity).
Learn more about negative acceleration