Which type of logic element uses a relay?

• A. Memory
• B. Timer
• C. Counter
• D. Input

Answer: (A)

Memory is about storing and keeping a state. In relay logic, that storage is achieved with a latch made from a relay coil and its own contacts. When the input energizes the coil, the contact closes and can feed back to keep the coil energized even after the original input drops, so the state is remembered. This latching action is how memory elements use relays. Timers and counters also use relays, but their main purpose is to time events or count pulses, not to indefinitely hold a state. An input is simply a signal source, not a storage element. So memory best fits the idea of a logic element that uses a relay to retain information.