The Buffer Solution in the Flask Was Prepared Using One

Short Answer

The buffer solution in the flask was prepared using one of the substances shown below.
citric acid (pK_a 3.08)
NaH₂PO₄ (pK_a 7.21)
NH₄Cl (pK_a 9.25)
Using the pH meter and solution shown in the image below, complete the following statements using one of the terms below.
increase
decrease
remain constant
citric acid
NaH₂PO₄
NH₄Cl
-The buffer solution in the beaker could be prepared using__________.