Final answer:
The correct conditional tense form of the verb 'poner' in the sentence 'Yo (poner) el libro en la mesa.' is 'pondría'.
Step-by-step explanation:
The correct conditional tense form of the verb poner in the sentence 'Yo (poner) el libro en la mesa.' is pondría. The conditional tense is used to express actions or events that would happen in the future under certain conditions. In this sentence, the verb 'poner' is conjugated in the first person singular form, which is 'pondría'.
Learn more about Spanish verb conjugation