Question

Consider a triprotic acid like phosphoric acid or citric acid. which expression correctly describes the relative magnitudes of the three ka equilibrium constants?

Answer 1

The triprotic acid like H₃PO₄ contains three protons H⁺ so it ionized through three steps, the acidity strength of first proton higher than second proton higher than third one so Ka1 > Ka2 > Ka3 But
For pKa which equals to -log Ka ... the higher the value of Ka, the smaller the value of pKa. so the correct answer will be:
pKa1 < pKa2 < pKa3