Who was john dalton?
a. a schoolteacher who published ideas about the atom
b. the scientist who discovered the electron
c. the physicist who came up with the oil-drop experiment
d. a physicist who studied the nucleus of the atom

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.