Janet is studying the element nitrogen (N). She wants to find the element whose atomic number is one greater than the atomic number of nitrogen. Which element is it?

- decrease the number of plants and animals living in the water.

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.