Final answer:
The addition of a fluorine substituent to a carbocation will increase the stability due to fluorine's high electronegativity and its inductive effect.
Step-by-step explanation:
The addition of a fluorine substituent to a carbocation will generally increase stability of the carbocation. Fluorine, being highly electronegative, can stabilize the positive charge through inductive effect by pulling electron density through sigma bonds, which diminishes the intensity of the positive charge on the central carbon atom. Carbocation stability increases in the order: primary (RCH₂⁺) < secondary (R₂CH⁺) < tertiary (R₃C⁺). Fluorine, due to its electronegativity and ability to disperse the positive charge, contributes to this increasing stability. Consequently, the correct answer to the question 'What effect will the addition of a fluorine substituent have on carbocation stability?' would be option (a) Increase Stability, as fluorine is highly electronegative and can stabilize the positive charge of the carbocation.