you add 6.4 g of iron to 26.90 mL of water and observe that the volume of iron and water together is 27.71 mL calculate the density of iron

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.

since electrons are negative the answer is neagtaive