Answer the following question given this paragraph: Magnetic resonance imaging (NMR) devices use liquid nitrogen to cool the superconducting magnets. Nitrogen is a gas at room temperature and liquefies at -195.8C. Its neighbor on the periodic table (oxygen) boils at -182.95C. The interactions between nitrogen molecules (N 2 ) are weaker, so the boiling point is lower. Interactions between non-polar molecules depend on the degree of electron fluctuation within the molecule. Q: Magnetic resonance imaging devices use what to cool the superconducting magnets? Choices: - antifreeze - dry ice - fluorocarbons - liquid nitrogen A:
liquid nitrogen