From the given options let's select the example which shows a conceptual model.
A conceptual model can be said to be a model which shows an abstract representation of any concept which can be visualized or imagined than other models.
It is a model which the designers want users to understand.
From the list, the best option which is an example of a conceptual model is a mental image of gas molecules as tiny balls.
Let's say, for example, you imagine or have a mental picture of gas molecules using your imagination, it helps to understand how a vacuum system works and you can easily solve the problem if something goes wrong.
Therefore, the example of a conceptual model is:
A mental image of gas molecules as tiny balls.
• ANSWER:
A. mental image of gas molecules as tiny balls