Which of the following is NOT a chemical change? A. Tarnishing silver
B. Melting butter
C. Digesting food
D. Baking a cake

Melting butter

Explanation:

You can reverse the change of butter back to its original state but you can never reverse the rest back to there original state

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.

50.23 i believe is correct but don't quote me on that.