Which gate outputs 1 when exactly one input is 1?

• A. XNOR Gate
• B. XOR Gate
• C. OR Gate
• D. AND Gate

Answer: (B)

The gate that outputs 1 when exactly one input is 1 is the exclusive OR gate. It produces a 1 whenever the two inputs are different, and a 0 when they are the same. For two inputs, the only cases that yield 1 are 0 and 1, or 1 and 0.

That matches the requirement of having exactly one input high. In contrast, the XNOR gate gives 1 when the inputs are equal (0 with 0 or 1 with 1), not when they’re different. The OR gate would output 1 for any case where at least one input is 1 (including both 1s). The AND gate outputs 1 only when both inputs are 1. So the exclusive OR is the correct choice for the described behavior. Note that with more than two inputs, XOR’s behavior changes to 1 when an odd number of inputs are 1, not strictly when exactly one is 1.