Your original sample of Manganese-56 is 20.0 mg. How much is left after 3 half lives? Remember to round to the correct number of significant figures and use units (mg).

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.