6. One sample has a chemical composition with a ratio of two iron atoms to three oxygen atoms. Another sample has a chemical composition with a ratio of three iron atoms to four oxygen atoms. They contain the same elements: Are they the same mineral?

They are not.

Explanation:

When it comes to molecular bonding, a single additional atom can change the characteristics of the compound. This is why Carbon Dioxide is different from Carbon Monoxide even though they both contain only Carbon and Oxygen atoms albeit in different quantities.

In this scenario the compounds described are Hematite which has two iron atoms to three oxygen atoms and Magnetite which has three iron atoms to four oxygen atoms. The presence of the different number of the same atoms made these compounds different.