Which device stores a single bit and has two stable states?

• A. Shift register
• B. Latch
• C. Flip-flop
• D. Register

Answer: (C)

A flip-flop is a bistable memory element that stores a single binary value and has two stable states, 0 and 1. It holds its state until a clock edge triggers a change, making it the standard building block for synchronous storage of one bit. A shift register is actually a chain of such memory elements used to store multiple bits and move them along with clock pulses. A latch can store one bit as well, but it is level-sensitive and changes with the input when enabled, not clock-edge triggered. A register is simply a group of flip-flops used to store multiple bits.