Final answer:
The word 'padre' correctly completes the sentence.
Step-by-step explanation:
The correct word that completes the sentence is padre. In the sentence, 'Él es mi tío, el de mi padre,' the word 'padre' means 'father.' Therefore, the sentence translates to 'He is my uncle, my father's...' and 'padre' is the appropriate word to complete the sentence.
Learn more about Completing sentences in Spanish