When an atom becomes an ion which subatomic particle undergoes a change in number in the atom

coral.

explanation:

coral. many marine organisms that produce calcium carbonate shells or skeletons are negatively impacted by increasing co2 levels and decreasing ph in seawater.

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.