Why do some compound have 1 hydrogen, some have 2 hydrogens, and some have 3 hydrogens?

answer: you could do some invislibe ink.

explanation: i will tell you how to if u answer my question.

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.