Final answer:
A proton surrounded by more electron density is deshielded and its NMR signal appears downfield. However, the question incorrectly associates more electron density with being shielded, which leads to an incorrect answer choice.
Step-by-step explanation:
When a proton has more electron density surrounding it, the proton is described as being deshielded. This occurs because there are more electrons between the proton and the surrounding environment, which increases the effective nuclear charge that the proton feels.
In nuclear magnetic resonance (NMR) spectroscopy, a deshielded proton is one that is more exposed to the external magnetic field, which in turn causes its resonant signal to appear downfield. So, if a proton has more electron density surrounding it, the correct answer would be b) shielded, downfield. However, because the question contains an internal contradiction regarding 'shielding' and 'electron density,' the answer as it is phrased is incorrect. A proton with more electron density surrounding it will actually appear deshielded, and move downfield on the NMR spectrum.