What must a flip-flop have in digital circuits?

• A. Data Input
• B. Clock
• C. Reset
• D. Output

Answer: (B)

A flip-flop is a storage element whose state updates only at specific timing events, controlled by a clock signal. That clock provides the timing reference that coordinates when the stored bit can change, which is essential for keeping all parts of a synchronous circuit in sync. With each clock edge, the flip-flop samples its input and may update its output, enabling predictable, coordinated behavior across a register or processor.

Data input and output are standard features of a flip-flop, and many designs include a reset to initialize or clear the stored bit. But the defining characteristic that makes it a flip-flop, as opposed to a simple latch, is the clock input that governs when changes are allowed.