Q.In a deque, if insertion and deletion of elements is done from the opposite end, it will behave as

This is an MCQ testing the behavioral equivalence of a deque under restricted operations.

A deque (double-ended queue) permits insertion and deletion at both ends. The question asks what happens when we enforce the discipline that insertions occur at one end and deletions at the opposite end.

Consider a deque where we insert at the rear and delete from the front (or equivalently, insert at the front and delete from the rear). An element inserted first will be the first to leave when we delete. This is precisely FIFO (First-In-First-Out) order, which defines a queue.

In contrast, a stack requires insertions and deletions at the same end, giving LIFO (Last-In-First-Out) behavior. A general list allows arbitrary positional access, which this restricted deque does not.

Why the other options are wrong:

• (2) Stack: A stack uses the same end for both push and pop. Here, opposite ends are used, so LIFO does not hold. …

A deque (double-ended queue) is a linear data structure that permits insertion and deletion at both ends. The question asks what happens when we restrict operations to opposite ends — specifically, when we insert at one end and delete from the other.

The key is to recognize the order in which elements are processed.

Understanding the behavior

Suppose we insert elements at the rear and delete from the front:

The first element inserted (A) is the first one removed. This is FIFO (First-In-First-Out) behavior, which defines a queue.

Contrast this with a stack, where insertion and deletion happen at the same end, giving LIFO (Last-In-First-Out) order. If we inserted and deleted both from the rear:

That would be stack behavior — but the question specifies opposite ends. …