Who organized elements into four groups based on properties:

What is the most common reason for matter changing its state?

What are two radioactive isotopes that are used for dating rocks that are older than 10 million years

How can a scientist assess whether a pure niobium (nb) sample is responsible for contaminating the lab with radioactivity? test the niobium sample to see whether it now contains other elements.test the niobium sample for the presence of niobium oxide compounds.heat the niobium, and see if the level of radioactivity in the lab increases.place the niobium under pressure, and see if the level of radioactivity in the lab increases.