Final answer:
Capacity is the necessary ingredient to form a contract from the options provided. It ensures that parties entering into a contract have the legal ability to do so, typically defined by age and mental competence. Therefore, the correct option is D) Capacity.
Step-by-step explanation:
The ingredient necessary to form a contract from the options provided is Capacity. Capacity refers to the legal ability of a party to enter into a contract. In most jurisdictions, this means that the person must have reached the age of majority (which is often 18), be of sound mind, and not be disqualified from contracting by any statute. Parties lacking capacity, such as minors, those not of sound mind, or intoxicated individuals, may not be able to enter into a legally binding contract.
In contrast, other options like exemption clauses, fairness, privity, and assignment are concepts related to the contents or characteristics of contracts, or how rights and obligations under a contract may be transferred or enforced, but they are not prerequisites for the formation of a contract.