GATE CS 2005 Q2 — Trees

An Abstract Data Type (ADT) is a mathematical model for data types where the data type is defined solely by its behavior (operations and constraints) from the user's perspective, independent of any specific implementation.

Let's analyze the options:

• Option C is correct: By definition, an ADT hides its internal data representation and implementation details. The user can only interact with the data type using the public operations defined in its interface, and nothing else.
• Option A is incorrect: An abstract class is a concrete programming language feature (such as in Java or C++) used to implement abstraction and inheritance. An ADT is a theoretical, language-independent concept.
• Option B is incorrect: ADTs can be instantiated. For example, a Stack is an ADT, and we can create multiple instances of a stack in our programs.

Therefore, the correct option is C.