How many moles of water (h2o) are present in a beaker containing 45.9 g h2o? give your answer to the correct number of significant figures.
(molar mass of water = 18.02 g/mol) 45.9 g h2o = mol h2o

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.