What is the maximum number of grams of PH, that can be formed when 3.03 g of phosphorus reacts with 3 03 g of hydrogen to form PH,?
P(g) + 6 Hug) - 4 PH,(g)

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.