In the titration of a monoprotic acid with a solution of sodium hydroxide of known concentration, what quantities are equal at the equivalence point?
(A) the concentrations of hydroxide and hydronium ions
(B) the number of moles of hydroxide ion added and the number of moles of hydronium ion initially present
(C) the volume of sodium hydroxide solution added and the volume of acid solution initially present
(D) the number of moles of hydroxide ion added and the number of moles of monoprotic acid initially present