A contract is an agreement
A contract is a legally binding agreement between two or more parties that creates obligations that are enforceable by law. It is a fundamental concept in contract law and is essential for the smooth functioning of business transactions. The Indian Contract Act, 1872 provides the legal framework for contracts in India.

Made by the parties who are competent to contract
One of the essential elements of a valid contract is the competence of the parties involved. Competence refers to the legal capacity of a person to enter into a contract. The Indian Contract Act specifies that parties to a contract must be competent to contract. In other words, they must be of sound mind, of legal age, and not disqualified by any law from entering into a contract. This ensures that the parties have the ability to understand the terms and implications of the contract and can be held legally responsible for their actions.

Not enforceable by law
This option is incorrect. A contract is, in fact, enforceable by law. When parties enter into a valid contract, they are legally bound to fulfill their obligations as per the terms of the contract. If one party fails to fulfill their obligations, the other party can seek legal remedies to enforce the contract and claim damages or specific performance.

Enforceable at the option of the aggrieved party
This option is incorrect. The enforceability of a contract does not depend on the option of the aggrieved party. Once a contract is validly formed, it is enforceable by both parties involved. If one party breaches the contract, the other party has the right to seek legal recourse and enforce the contract.

Made without free consent and consideration
This option is incorrect. For a contract to be valid, it must be made with free consent and consideration. Free consent means that the parties involved have given their consent to the contract without any undue influence, coercion, fraud, or misrepresentation. Consideration refers to something of value that is exchanged between the parties, such as money, goods, or services. Both free consent and consideration are essential elements of a valid contract.

In conclusion, the correct answer is option 'A' - a contract is an agreement made by the parties who are competent to contract. The parties must have the legal capacity to enter into a contract, and the contract must be made with free consent and consideration. Additionally, a contract is enforceable by law and not dependent on the option of the aggrieved party.