How do insertion and removal orders differ between a stack and a queue?

How do insertion and removal orders differ between a stack and a queue?

• A. Stack is FIFO; Queue is LIFO
• B. Stack is LIFO; Queue is FIFO
• C. Both are LIFO
• D. Both are FIFO

Answer: (B)

In a stack, you push items onto the top and pop them off the top, so the most recently added item is the first one removed. That behavior is called LIFO (last in, first out). In a queue, you enqueue items at the back and dequeue from the front, so items leave in the order they arrived—FIFO (first in, first out). This is why the correct description is that the stack operates with LIFO while the queue operates with FIFO. The other descriptions mix up the orders or claim both structures use the same rule, which doesn’t fit how stacks and queues manage insertion and removal. A quick intuition: a stack is like a stack of plates you can only take from the top; a queue is like people waiting in line, served in the order they arrived.