The decreasing order of acidity of the marked H of the following molecules is A. I > II > III B. III > I > II C. III > II > I D. II > I > III

The correct answer is: C. III > II > I

The acidity of a molecule is determined by the stability of the conjugate base. The more stable the conjugate base, the weaker the acid.

In the given molecules, the conjugate bases are:

• I: $\ce{R-CH2-COO-}$
• II: $\ce{R-CH(OH)-COO-}$
• III: $\ce{R-CH(NH2)-COO-}$

The conjugate base of III is the most stable because it has the most resonance structures. The conjugate base of II is less stable because it has one less resonance structure. The conjugate base of I is the least stable because it has no resonance structures.

Therefore, the acidity of the molecules decreases in the order III > II > I.