Which access modifier restricts a variable's access to within the class itself?

The access modifier that restricts a variable's access to only within the class itself is known as Private. When a variable is declared as Private, it means that it cannot be accessed from outside the class where it is defined. This encapsulation is a fundamental principle in object-oriented programming, ensuring that the internal state of an object is protected from unintended interference and misuse by other parts of the program.

By using private access, you effectively create a controlled environment for the class, allowing it to manage its own data securely. This means that any manipulation of the private variable must be done through public methods or properties within the class, providing opportunities to implement validation or other logic as needed when interacting with that data.

The other access modifiers have different scopes of access: Public allows access from anywhere, Protected permits access within the class and by derived classes, while Internal grants access to variables within the same assembly (namespace or module). Therefore, private is the correct choice for limiting access strictly to the class itself.