Which of the following mixtures will result in the formation…

Which of the following mixtures will result in the formation of an effective buffer? 0.020 moles hydrofluoric acid, HF and 0.001 moles sodium fluoride, NaF. 0.040 moles ethylamine, CH3CH2NH2 and 0.030 moles ethylammonium bromide, CH3 CH2NH3Br. 0.030 moles formic acid, HCOOH and 0.020 moles sodium hydroxide, NaOH. 0.050 moles nitric acid, HNO3 and 0.030 moles sodium nitrate, NaNO3.