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The strongest acid among the three options is:

 Cl-CH2-COOH (chloroacetic acid)

Here's the reasoning behind this answer:

Acidity Strength: Acidity strength is directly related to the stability of the conjugate base formed after losing a proton (H+). A more stable conjugate base leads to a weaker bond between the hydrogen and the remaining molecule, making it easier to lose the proton and hence a stronger acid.

Electron-withdrawing effect: Chlorine (Cl) is an electron-withdrawing group. When attached to the carbon atom next to the carboxylic acid group (COOH), it pulls electron density away from the oxygen atoms in the group. This makes the O-H bond weaker and easier to break, stabilizing the conjugate base (CH2-COO-) and increasing the acid strength.

Resonance stabilization: In chloroacetic acid, the negative charge on the conjugate base can be delocalized (spread out) through resonance across the chlorine atom and the oxygen atoms in the COO- group. This further stabilizes the conjugate base and strengthens the acid.