A queue follows _______.

Question

Accepted Answer

The correct option is (1):
FIFO (First In First Out) principle is the defining characteristic of a Queue data structure. A queue is a linear collection of elements that is conceptually modeled after a real-world line, such as customers waiting for service. The acronym FIFO explicitly describes its behavior: the element that is inserted *First* into the queue is always the element that comes *First Out*. Data is consistently added at one end, called the **Rear** or **Tail** (the *enqueue* operation), and removed from the opposite end, called the **Front** or **Head** (the *dequeue* operation). This strict, two-ended, sequential ordering is what makes queues indispensable in applications like operating system process scheduling and managing print jobs, ensuring fairness and chronological execution.

The incorrect option is (2):
LIFO (Last In First Out) principle is the operational rule for a **Stack** data structure, not a queue. This principle dictates that the most recently added element is the first one to be removed, similar to a stack of plates where the last one placed on top is the first one taken off. This is the exact opposite of the FIFO behavior that defines a queue, as all insertions and deletions in a stack occur at a single point, known as the **Top**. Therefore, LIFO describes a completely different and distinct abstract data type.

The incorrect option is (3):
Ordered array is a means of implementation, not a governing operational principle. An array is a physical, contiguous memory structure that can be used to store a queue's elements, but it is not the conceptual rule that defines how a queue behaves. Moreover, the definition of a queue (FIFO) is independent of whether it is implemented using an array or a linked list, and the queue itself is an Abstract Data Type defined by its set of operations.

The incorrect option is (4):
Linear tree is a contradictory term in the field of data structures. A queue is classified as a **linear** data structure because its elements are arranged in a sequence. Conversely, a **tree** is fundamentally a **non-linear** data structure, characterized by its hierarchical (parent-child) relationships and branching structure. Since a queue's structure is sequential and its access pattern is simple, it cannot be described as a tree, which is a complex, branching structure.