The correct answer is option 3: a writ.

In the context of fundamental rights, a writ is a legal document issued by a court that directs a government or public authority to perform a specific action or refrain from doing something that is violating an individual`s fundamental rights. It is a mechanism through which the court ensures the enforcement and protection of fundamental rights.

A decree (option 1) is a final decision or order given by a court in a civil case, usually involving disputes between private parties. It is not specifically related to the enforcement of fundamental rights.

An ordinance (option 2) is a law or regulation issued by a government authority, usually at a local or municipal level. It is not typically used to enforce fundamental rights.

A notification (option 4) is a formal announcement or notice made by a government or public authority. It is not directly associated with the enforcement of fundamental rights.