NextStep Chemistry

The kinetics of the ninhydrin reaction were shown to be first order with respcct Io 1,2,3-indantrione and a-alpha amino acid, and second order overall. The reaction rate was shown to vary with solution pH. The initial reaction rate was greatest when the product of which two concentrations was maximized? (Note: R=C'H4O2.)

A. [RC=O+H] [H2NCHRCOO-]
B. [RC=O] [+H3NCHRCOO-]
C. [RC=O+H] [+H3NCHRCOOH]
D. [RC=O] [H2NCHRCOOH]

Here is the explanation, i am not understanding why RC=OH+ is a better...

NextStep Chemistry