What is the molarity of a solution with 2.1 mol of HCl in 400 mL of water? (M = mol/L)
A.) 0.00525 M
B.) 5.25 M
C.) 190 M
D.) 2.1 M

they are made of gases.

they have a spherical shape.

they make energy through fusion.

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.