The oxidation number of all the element in free state is 0​

Zero-Nine

Explanation:

this is becasue these numbers are rather small and if you plug these numbers into an equation you will most likely get 0.

14 days is the half-life of phosphorus-32

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.