What does an atomic number represent in an atom

It represents the number of protons in the nucleus of an atom which determines the chemical properties of an element.

i think it is d. e because the next one is igneous.

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.