Final answer:
The singular form of the third declension adjective 'potens, potentis' is potens.
Step-by-step explanation:
The singular form of the third declension adjective 'potens, potentis' is potens.
So, the correct answer is option 4) potentia.
When declining third declension adjectives, the form 'potens' is used for both the nominative and accusative singular cases.