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.

The correct option is to test the sample of niobium for the existence of niobium oxide compounds.

Explanation:

Columbium, now known as niobium refers to a chemical element exhibiting the symbol Nb, with atomic number 41. It is a light grey, strong, ductile, and a crystalline transition metal.  

In the given question, contamination cannot be determined with the presence of niobium oxide compounds as niobium oxides are not radioactive, and both the temperature and pressure do not influence the rate of decay. Thus, the last three given options are irrelevant. Hence, the only correct method would be to test the niobium sample to see if it contains any other kinds of elements.

answer by yourhope:

how do models compare to real-world objects?

d. most models represent a real-world object in a simpler way.

: )

a polar bond is formed when electrons are shared unevenly between atoms