What is required for a valid contract under Illinois law?

A valid contract under Illinois law requires an offer, acceptance, consideration, and a lawful purpose. The foundational elements of a contract ensure that there is a mutual agreement between the parties involved, but also include consideration, which is something of value exchanged between the parties. Without consideration, a contract typically wouldn't be enforceable, as it signifies that each party is providing something of value in the agreement.

Additionally, the requirement for a lawful purpose ensures that the contract is not for an illegal act or against public policy, which would render the contract void. This comprehensive view encompasses the essential aspects that form a legally binding agreement, making option B the correct choice in this context.

In contrast, while an offer, acceptance, and mutual agreement are necessary components of a contract, they do not encompass consideration and the lawful purpose, which are critical for validity under Illinois law. Written documentation might be required for certain types of contracts (such as real estate transactions), but it is not a blanket requirement for all contracts under Illinois law. Similarly, the signature of two witnesses is not a standard requirement for the validity of contracts in general, although it may be necessary for specific types of agreements, such as wills.