How can a scientist assess whether a pure niobium sample is responsible for contaminating the lab with radioactivity

c)as speed changes, wavelength and frequency change.

everything changes!

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.