What defines a unilateral contract?

A unilateral contract is characterized by a single promise that is contingent upon the performance of a specific act by one party. In this type of contract, one party makes a promise in order to induce the other party to perform, but only the party receiving the promise is required to fulfill their part of the agreement through their actions. For instance, a reward offer for the return of a lost item exemplifies a unilateral contract; the person offering the reward is only obligated to fulfill their promise upon receiving the item, while the person returning the item does not need to make any promise in return.

The options about the exchange of promises and mutual consent refer more to bilateral contracts, where both parties exchange promises to perform certain obligations. An agreement in writing is a general requirement for many types of contracts but does not specifically delineate unilateral contracts from others. Thus, the defining characteristic of a unilateral contract is indeed a single promise in exchange for performance, which makes the choice that states this definition accurate.