Which of the following is NOT an essential element of a valid contract?

A valid contract requires several essential elements to be legally enforceable. Among these elements are an agreement between parties, which encompasses an offer and acceptance; genuineness of assent, meaning that all parties involved must genuinely agree to the terms of the contract without duress or misrepresentation; and legality, indicating that the subject matter of the contract must be lawful and not go against public policy.

The option indicating a formal written contract is not an essential element for all valid contracts because many contracts can be oral and still legally binding, provided they comply with relevant laws (such as the Statute of Frauds, which specifies certain contracts that must be in writing). Thus, while a written contract can serve as strong evidence of the agreement and its terms, it is not inherently required to validate the existence of a contract.