Final answer:
The verb mood in the given sentence is the subjunctive mood.
Step-by-step explanation:
The verb mood used in the sentence "If I were rich, I would buy a yacht" is the subjunctive mood.
The subjunctive mood is used to express wishes, suggestions, or requirements, or to state hypothetical or unlikely conditions.
In this sentence, the speaker is imagining a hypothetical situation where they are rich and expressing what they would do in that case.
The use of "were" instead of "was" with the pronoun "I" is a key indicator of the subjunctive mood.