What accurately describes an astable multivibrator?

An astable multivibrator is accurately described as a circuit that alternates between two unstable states. This type of circuit continuously oscillates without requiring any external triggering, making it inherently unstable. As it switches between the two states, it generates a square wave output, which can be useful in a variety of applications such as timing circuits, clock pulses, and waveform generation.

The essential characteristic of an astable multivibrator is that it does not have any stable states; instead, it transitions between high and low outputs continuously. This behavior is fundamentally different from circuits that have stable states, such as bistable multivibrators, which can hold a state until triggered to change.

The other options describe different functions or characteristics that do not apply to astable multivibrators. For instance, a circuit that stabilizes voltage refers to a voltage regulator rather than an astable multivibrator, and a circuit that switches states once characterizes a monostable multivibrator. Similarly, a circuit that has one stable state describes a bistable multivibrator, which is distinct from the continuous oscillation behavior exhibited by an astable multivibrator.