Solve this The first one is the Bromine water test
the second is the Baeyers test
Third is addition reaction

1 CH3-CHBR-CH2BR

2.CH3-CH2-CH3

3.CH3-CHCL-CH2CL

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.