What type of relay is used where the state changes after a specific time period?

The correct choice is a delay relay, which is designed to alter its state after a predetermined time period. This type of relay is commonly used in various applications requiring timed control, such as in starting or stopping motors, or delaying an action in an electrical circuit.

Delay relays can be configured to activate after a set time delay, making them ideal for systems where a delay is necessary for proper operation. For example, if a motor requires a few seconds before it receives power to allow for other components to stabilize, a delay relay would be incorporated in the circuit to manage this timing effectively.

In contrast, a one-shot relay typically activates just once in response to a triggering input and does not continue to maintain its state. Reset relays are used to reset a circuit or device, often returning it to a default state, rather than maintaining a status based on a time delay. Instant relays, as implied by the name, operate without any time delay and react immediately to input signals.