Which of the Following Is Not a Buffer System? a Solution

Multiple Choice

Which of the following is not a buffer system? A solution containing roughly equal concentrations of ________

A) fluoride ion and hydrofluoric acid.
B) bromide ion and hydrobromic acid.
C) phosphate ion and hydrogen phosphate ion.
D) carbonate ion and hydrogen carbonate ion.
E) phosphoric acid and dihydrogen phosphate ion.