What type of signal has only two states: ON and OFF?

• A. Analog
• B. Digital
• C. Discrete
• D. Pulse

Answer: (C)

Two-state ON and OFF signals are binary in nature. They behave like a switch that is either fully on or fully off, with no in-between values. In practice this is described as a digital signal, where the two distinct voltage levels represent logic states (for example, high for ON and low for OFF). This two-level, discrete representation is what makes digital signals easy for controllers to interpret reliably, even in the presence of some noise, because a clear threshold separates the ON state from the OFF state.

It’s useful to contrast with other terms: a discrete signal refers to when the signal is defined at separate moments in time, which can apply to many kinds of signals, including those with more than two levels. A pulse is a brief transient event and isn’t inherently a sustained ON/OFF representation. So the feature that truly defines two-state signaling is the digital, binary nature, not merely discreteness in time or a fleeting pulse.