Please choose the correct answer to the question: Two pieces of the same metal are placed on a table. The pieces of metal have the same density, mass, and texture. Which characteristic must be the ONLY difference between the two samples?

Answer1: They have different dimensions. Answer2: They have different boiling points. Answer3: They are made up of a different type of matter. Answer4: They contain a different amount of matter per unit volume.

Answer format: answer1/answer2/answer3/answer4