Which logic gate outputs a 0 when all inputs are 1, effectively the inverse of an AND gate?

• A. AND gate
• B. OR gate
• C. NOT gate
• D. NAND gate

Answer: (D)

Think about what happens when every input is high. An AND gate gives a high output only if all inputs are high. If you invert that result, you get a high output except when all inputs are high, at which point it becomes low. That inverted behavior is exactly what a NAND gate does. For two inputs, when both are 1, AND would be 1, and NAND becomes 0; for any other input combination, NAND outputs 1. This differs from the OR gate, which would be 0 only when all inputs are 0, and from the NOT gate, which only handles a single input. So the gate that outputs 0 when all inputs are 1 is the NAND gate.