How many grams of iron are present in 150. g of the alloy

An alloy of iron contains 75.0% iron and 25.0% other elements. so it has 113 grams                          

"the periodic table is arranged in order of atomic number."

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.