* What happens when elements chemically combine?
1) All elements retain their original properties
2) New properties are formed
3) Only metals retain their original properties
4) New elements are formed

*tilts head* sounds more like a statement

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.