Acid Dissociation Constants

Step 1: Understanding Dissociation Constants.
Phosphoric acid ( ) is a triprotic acid, meaning it dissociates in three steps. Each step has a dissociation constant: . The first dissociation constant ( ) is the strongest, as phosphoric acid dissociates more easily to form . The second dissociation constant ( ) is smaller because it involves the dissociation of to , which is less acidic. The third dissociation constant ( ) is the smallest since dissociates very weakly to form .

Step 2: Conclusion.
Therefore, the dissociation constants for phosphoric acid are arranged in the order , which matches option (2).

Final Answer: