Explain why all models have limitations.

All models have limitations because they are not representative of every possible scenario. They use current knowledge and scientific data, but as those are subject to change, the models based off that knowledge and data are subject to change as well

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

it means there are 3 atoms of oxygen