Final answer:
Magnetic Resonance Imaging (MRI) requires hydrogen nuclei, abundant in water molecules in soft tissues, to work properly.
Step-by-step explanation:
Magnetic Resonance Imaging (MRI) requires the biological molecule known as hydrogen nuclei to work properly. Hydrogen nuclei, which are abundant in the water molecules found in soft tissues, are subjected to fluctuating magnetic fields in the MRI machine. These magnetic fields cause the hydrogen nuclei to emit their own magnetic signals, which are then read and interpreted by sensors in the machine to create detailed images.