An inverter (NOT gate) has only how many input(s)? The output is always the logical complement of that input.

Introduction / Context:
The inverter, also called a NOT gate, is one of the most basic logic elements. It flips the logic level: 0 becomes 1, and 1 becomes 0. Understanding its arity (number of inputs) and behavior is essential for building and analyzing combinational and sequential circuits.

Given Data / Assumptions:

• The device discussed is an inverter/NOT gate.
• “Logical complement” means output = 1 when input = 0, and output = 0 when input = 1.
• We are referring to standard digital logic families (TTL, CMOS) where inverter symbols have a single input bubble output.

Concept / Approach:
An inverter is defined as a single-input gate. Formally, its Boolean function is Y = NOT(A), often written as Y = A′ or Y = ~A. Multi-input gates that produce complements exist (e.g., NAND, NOR), but those are not called inverters; they implement complements of multi-input functions. The minimal inverter requires only one input to produce the complement at its output.

Step-by-Step Solution:
Identify the gate: NOT (inverter).Recall the function: Y = NOT(A).Count inputs: exactly one input variable A.Therefore, choose “one.”

Verification / Alternative check:
Look at logic symbols: a triangle (buffer) with a small circle (inversion bubble) on the output represents an inverter with a single input pin. Datasheets list 6 inverters per IC (e.g., 74HC04) each with one input and one output.

Why Other Options Are Wrong:
Two or more inputs defines different gates (e.g., NAND, NOR, AND, OR). “All of the above” cannot be correct because the definition is specific. “None” is wrong since “one” is correct.

Common Pitfalls:
Confusing an inverter with a buffer (which does not invert); assuming a “universal” NAND/NOR gate is the same as an inverter—those require tying inputs together to mimic a single-input inversion, but they are not inverters by definition.

Final Answer:
one