<prompt> Action of a buffer is maximum when its pH ispKapKIp loghpI  <response>: Ans: a pKaRef: Vasudevan Sreekumari, 6th edi., Pg. 340BUFFERS - are solutions which can resist changes in pH when acid or alkali is added.Composition of buffers - two typesMixtures of weak acid with their salt with a strong base. Mixture of weak bases with their salt with strong acid.Example-Carbonic acid and sodium bicarbonate bicarbonate bufferAcetic acid and sodium acetate acetate bufferHENDERSON -HASSELBALCH EQUATIONpH pKa log pH negative log of hydrogen ion concentration pKa pH at which the acid is half ionized is called pKa of an acid When base or salt acid, then pH pKa Therefore, when the concentrations of bases and acid are same, then pH is equal to pKa. Strong acids will have a low pKa and weak acids have a higher pKa.A buffer is most effective when the concentration of salt and acid are equal or when pH pKa. When the ratio between salt and acid is 10:1, the pH will be 1 unit higher than the pKa. 