Is a pail of garbage a element ,compound or mixture?

A pail of garbage is a mixture. To figure out how and why it is, you need to understand what each of these things are. If it was an element, it would have a symbol and be on the periodic table of elements. If it was a compound, it would be a mix of two or more elements chemically combined. The reason it's a mixture is because there is no symbol for it, and you can PHYSICALLY separate it. Hope that makes sense! :)

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.