To observe means to gather
factual information about your
surroundings using your

1. they vary with a higher number because boiling is way hotter than melting

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.

a corroding iron, if that's one of your choices