Which of these elements has the smallest radius?
A. Si
B. Ar
C. Mg
D. S

i think it is of

(Magnesium)

hope it helps

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.