Which of the compounds shown below is much more acidic than the others? Provide a brief explanation for your answer.

Compound A.
Compound A is an aromatic compound. Therefore, it will lose a proton readily to maintain its aromatic character.

Compound B.
An aromatic anion is formed when compound B loses a proton. Therefore, compound B will lose a proton most easily.

Compound C.
A resonance stabilized anion is formed when compound C loses a proton. Therefore, compound C will lose a proton most easily.

Compound D.
An extended conjugation system is formed when compound D loses a proton. Therefore, compound D will lose a proton spontaneously.