**Competent Parties**

A contract requires competent parties, which means that both parties involved in the contract must have the legal capacity to enter into a contract. This typically means that they must be of legal age, mentally sound, and not under the influence of drugs or alcohol. If one or both parties lack the legal capacity to enter into a contract, the contract may be considered void or voidable.

**Free Consent**

Free consent is essential for a contract to be valid. It means that both parties must enter into the contract willingly and without any undue influence, coercion, fraud, misrepresentation, or mistake. If consent is obtained through any of these means, the contract may be considered voidable.

**Lawful Consideration**

A contract must involve lawful consideration, which means that both parties must exchange something of value as part of the contract. Consideration can be in the form of money, goods, services, or a promise to do or not do something. If there is no consideration involved, the contract may be considered void.

**Reasonable Terms and Conditions**

Reasonable terms and conditions are not necessary for a contract. While it is generally advisable to have clear and reasonable terms and conditions in a contract to avoid misunderstandings and disputes, the absence of reasonable terms and conditions does not make a contract invalid. As long as the contract meets the other essential elements, such as competent parties, free consent, and lawful consideration, it will still be legally binding.

Furthermore, what may be considered reasonable can vary depending on the specific circumstances and the nature of the contract. What may be considered reasonable in one situation may not be reasonable in another. Therefore, the absence of reasonable terms and conditions does not invalidate a contract.

In conclusion, of the given options, the element that is not necessary for a contract is reasonable terms and conditions (option B). The other elements, such as competent parties, free consent, and lawful consideration, are essential for a contract to be valid and legally binding.