Which gate outputs true only when exactly one of its inputs is true?

The XOR (exclusive OR) gate is designed to output true (or high) only when exactly one of its inputs is true. This makes it particularly useful for situations where a binary choice is being made between two conditions. In other words, if you have two inputs, the XOR gate will yield a true output only when one input is true while the other is false. If both inputs are either true or false, the output will be false.

For example, if Input A is true and Input B is false, the output will be true. Conversely, if both are true or both are false, the output will be false. This unique behavior distinguishes the XOR gate from other types of gates, thus making it the correct answer for the question regarding a gate that outputs true when exactly one input is true.

In contrast, an AND gate requires both inputs to be true for its output to be true, a NOR gate outputs true only when all inputs are false, and a NAND gate provides a false output only when both inputs are true. Each of these gates serves different logical functions in digital circuits.