Lack of legal capacity makes a contract:

The correct choice indicates that a contract is relatively null when one party lacks legal capacity. Legal capacity refers to the ability of individuals to enter into a binding contract, which usually requires them to be of sound mind, of legal age, and not under duress or undue influence.

When a party lacks legal capacity, the contract is not automatically void; rather, it is considered relatively null. This means that while the contract may have some enforceable elements, the party lacking capacity can seek to have the contract annulled. For instance, if a minor enters into a contract without parental consent, that contract is generally considered relatively null at the option of the minor. This approach protects individuals who may not fully understand the ramifications of their actions or are unable to make informed decisions.

In contrast, other choices suggest that the contract could be fully enforceable, legally binding, or simply ineffective in negotiation. These interpretations do not adequately address the nuances of how a lack of legal capacity impacts the enforceability of contracts. By classifying such a contract as relatively null, the law provides a mechanism for protecting vulnerable parties and ensuring that agreements reflect the intention and legal ability to engage in those agreements.