Which element is essential for the formation of a valid contract?

The essential element for the formation of a valid contract is mutual consent and an offer. In contract law, mutual consent refers to the agreement between parties to enter into a contract, typically demonstrated through an offer by one party and acceptance by the other. The offer must be communicated clearly, allowing the offeree to understand the terms and respond affirmatively.

While a written document signed by both parties can help in evidencing the existence of a contract, it is not a requirement for validity in all cases. Many contracts can be valid even if they are oral, as long as the essential elements of the contract, including mutual consent, are met.

Witnesses present at the time of signing can add credibility or serve as evidence in case of disputes, but their presence is not a requirement for a contract to be valid. Similarly, immediate payment is not necessary for a contract's validity; parties can agree to different terms regarding payment timing, and a valid contract can exist even with deferred payment agreements.

Thus, mutual consent and an offer are foundational elements that must exist for a valid contract, making this the correct choice.