The output of a tristate buffer when the enable input is 0 is:

Concept: A tristate (3-state) buffer supports three output conditions, not just two: logic 0, logic 1, and a high-impedance (floating) state in which the output stage is switched off entirely — drawing no current and imposing no voltage on the line. This third state exists so many tristate outputs can share one common bus, since only the enabled driver may actively drive the line at any instant.

Application: Here the enable input is 0 (inactive). With the enable input low, the buffer's internal output-drive circuitry is switched off completely — neither a 0-path nor a 1-path is active. The output pin is therefore not forced to either logic level; it floats, electrically disconnected from the buffer, which is exactly the third state above.

Contrast with the other options:

• “Always 0” or “Always 1” would need the buffer to actively pull the line to a fixed level even while disabled — but a disabled tristate output drives nothing at all.

• “Retains the last value” describes a latch or flip-flop with memory; a tristate buffer is purely combinational and has no storage element to hold a past output.

• The output is instead floating/disconnected — neither driven to 0 or 1 nor holding any remembered value — which is why the disconnected (high-impedance) state is correct.

Why this matters: On a shared bus, every buffer except the one selected keeps its enable at 0 so its output floats; only the single enabled buffer drives the bus. If disabled buffers instead forced a fixed value or held old data, multiple devices sharing the bus would conflict.