Bob grants his sister Mary an estate for as long as she lives without the right to pass it to heirs. What type of estate is this?

The type of estate described in the question is a life estate, specifically an ordinary life estate. In this scenario, Bob grants Mary the right to possess and use the property for as long as she is alive. The key characteristic of a life estate is that it is limited in duration to the life of the person holding the estate—in this case, Mary.

Since Mary does not have the right to pass the estate to her heirs, this further reinforces the nature of a life estate. When the life tenant (Mary) passes away, the property will revert back to Bob or his estate if Bob has not specified any other arrangement.

Understanding the definition and implications of a life estate helps clarify why this is the correct answer. A fee simple estate, on the other hand, represents the most complete interest one can have in real property and includes the right to transfer it to heirs, which does not apply here. A leasehold estate involves renting or leasing property for a specified term and does not have the same indefinite ownership rights as a life estate. Lastly, a joint tenancy estate involves co-ownership with the right of survivorship, which is not relevant in this situation. Therefore, the ordinary life estate is the appropriate classification for this arrangement between Bob and Mary