What characterizes a unilateral contract?

A unilateral contract is characterized by a promise made by only one party, creating an obligation that is contingent upon the performance of a specific act by the other party. In such contracts, one party (the promisor) makes a commitment to do something, while the other party (the promisee) is not obligated to act or respond in any specific manner unless they choose to fulfill the condition of the contract. For example, in a reward scenario where one party offers to pay a sum of money to anyone who finds and returns a lost pet, the offeror (promisor) is bound by their promise only when someone (the promisee) completes the act of returning the pet.

The other options suggest characteristics of different contract types. A contract with mutual promises would be a bilateral contract, where both parties are obligated to perform their respective promises. An expressed oral agreement refers to the form in which a contract might be presented (either verbally or in writing) but does not define the nature of the obligations involved. Hence, the essence of a unilateral contract distinctly lies in the one-sided promise aspect, which is what option B represents.