In the troposphere of Titan. Saturn's largest moon, the atmospheric pressure is about 1.5 bar. At this point in the atmosphere there is approximately 4.996 methane (the vast majority of the atmosphere is nitrogen) by number. Calculate the partial pressure of methane in the stratosphere of Titan.​

i'm assuming that the correct answer is indeed the first one/ "a"..

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.