Final answer:
The stability of the negative charge in an acid, which affects acid strength, is related to the ability to delocalize charge, particularly through aromaticity, rather than molecular weight, solubility, or density.
Step-by-step explanation:
When you're comparing acidic strengths based on the relative stability of the negative charge formed by the removal of an acidic hydrogen, stability is related to factors such as inductive effects, ability to delocalize charge, and the strength of the bond between the hydrogen atom and the rest of the molecule. Specifically, aromaticity can greatly stabilize the conjugate base by delocalizing the negative charge over a cyclic, resonating structure.
Molecular weight, solubility, and density do not directly affect the stability of the negative charge or the acidic strength in this context.