In a magnetic flowmeter, the process fluid -----

In a magnetic flowmeter, the process fluid acts as the moving conductors due to its conductive properties when placed within a magnetic field. The fundamental principle behind a magnetic flowmeter is Faraday's law of electromagnetic induction, which states that a voltage is induced in a conductor moving through a magnetic field. In this case, the conductive fluid serves as the conductor while flowing through the magnetic field generated by the flowmeter's coils. As the fluid flows, it generates a voltage proportional to the flow rate, allowing for accurate measurement of the fluid's velocity.

The other options do not accurately describe the function of the process fluid within a magnetic flowmeter. The fluid does not need to be chemically reactive, artificially heated, or devoid of solids to utilize this measuring technology effectively. However, the conductivity of the fluid is crucial for the flowmeter to operate correctly, making the property of acting as a moving conductor the essential feature of the process fluid in this application.