When I saw this question, I thought RAP would apply to the Son’s executory interest because the “so long as used for farming” could happen more than 21 years in the future – does it not? So I thought the RAP would void the executory interest to Son, leaving just the devise to brother so long as used as a farm, voiding the Son’s interest, leaving a possibility of reverter in Widow? Which, Son could inherit?
Your RAP concern is reasonable, but the brother is a validating life here.
The son’s executory interest would become possessory when the brother stops using Blackacre for farming. That must happen during the brother’s lifetime or, at the latest, when he dies, because the condition is phrased as “so long as he uses” the land. It cannot remain unresolved for more than 21 years after the brother’s death. Therefore, the son’s executory interest is valid under RAP. Executory interests are subject to RAP, but this one satisfies it because the brother serves as the measuring life.
So the answer remains C: The son has an executory interest.
If the language instead said, “so long as the land is used for farming, then to my son,” the result might be different because the land could continue being farmed indefinitely after the brother’s death. In that case, RAP would be a much stronger objection.
If the son’s interest were invalid, the widow would retain a possibility of reverter, which could potentially pass to the son through the widow’s estate. But that is not what happens under this wording.