Question

If polyacidic bases dissociate in one step in aq. sol. , then why do they form different salts ( basic salts) on reacting with acids?

Answer 1

The formation of different salts on reaction with acids depends on the strength of acids used.

The polyacidic bases dissociates in water. That is simply the dissociation reaction.
But in the case of reaction with acids, the reaction depends on the strength of acids and bases.

If the acid is stronger, then the reaction would be faster and effective.
As the strength decreases, the reaction becomes slow, and the formed salts would be different.

Hope this helps.
Good luck.