How many fe(ii) ions are there in 10.0 g of feso4?

Iron sulfate can be shown as FeSO4 and the number mole of FeSO_4  can be determined as

Molar mass of Iron sulfate = 151 g /mole

Mass of Iron sulfate = 10 g

Number of Fe ion  can be determined as

Thus, ions are present in Iron sulfate

clouds form

solid ice forms on leaves.

water droplets form on grass.

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.