Which of the following are considered pure substance? ?
a. element
b. compound
c. homogenous mixture
d. heterogeneous mixture

Explanation:

I’m 99.9% sure that it’s an element because it can’t be broken down any more than it already is.

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.