Differentiate between a stack and a queue.

• A. Stack uses LIFO; Queue uses FIFO.
• B. Queue uses LIFO; Stack uses FIFO.
• C. Stack stores data; Queue stores instructions.
• D. Queue supports random access.

Answer: (A)

The key idea is how removal order relates to insertion order. A stack follows LIFO—last in, first out. You push items on top and pop from the top, so the most recently added item comes off first. A queue follows FIFO—first in, first out. You enqueue items at the back and dequeue from the front, so the oldest item added leaves first.

This distinction explains why the statement that a stack uses LIFO while a queue uses FIFO is the correct description. Stacks are great for things like tracking nested calls or undo stacks, where you want to unwind in the reverse order of how things were added. Queues are ideal for processing tasks in the order they arrive, such as print jobs or event handling, where you want to serve items in their arrival sequence.

The other options don’t fit: a stack and a queue both store data items, not a special category like instructions; and a queue typically doesn’t support random access, since you usually can only access the front (and maybe the rear) in a FIFO manner.