Which has the most buffering capacity at ph -6?
a. a 100mm solution of phosphate
b. a 1 mm solution of histidine
c. a 10 mm solution of glutamate
d. a 1m solution of alanine
e. they are all equal in their buffering capacity at ph 6

D. A 1M solution of Alanine

Explanation:

Buffering capacity is the capacity of a solution or substance to change the Ph of another substance when added to it in 1, so the buffering capacity of all of them, since they have the same Ph, would depende solely on the amount of moles os the given substance that you will add, in this case the substance that has the most matter would be D. A 1M solution of Alanine, that option would have the most buffering capacity since it is a full mole of matter.

gold i'm pretty sure i might be wrong