The correct option is D Nature of solvent
Factors affecting nucleophilicity
Charge density :
Higher the electron density, higher is the nucleophilicity.
Stability of nucleophile :
For two charged nucleophiles with the same nucleophilic site but bonded to different groups, the one with a lower stability is a better nucleophile.
Steric hindrance :
Nature of Solvent
Nucleophilic strength also depends on the type of solvent used. For example:
F− will act as a strong nucleophile in polar aprotic solvent but it act as weak nucleophile in polar protic solvent due to very high solvation of F− by H+ ions in polar protic solvent.