Which statement correctly describes a NOR gate?

Which statement correctly describes a NOR gate?

• A. Outputs true whenever any input is true.
• B. Outputs true only when all inputs are true.
• C. Outputs true only when all inputs are false.
• D. Outputs true when at least one input is false.

Answer: (C)

A NOR gate is the negation of the OR of its inputs. It outputs true only when every input is false because OR would be false when all inputs are false, and inverting that gives a true output. If any input is true, the OR result is true, and the NOR output becomes false. For two inputs, both false yields a true output; any true input yields a false output. This behavior matches the statement that outputs true only when all inputs are false. The other common gate behaviors—outputting true whenever any input is true (OR), outputs true only when all inputs are true (AND), or outputs true when at least one input is false (NAND in a broader sense)—do not describe NOR.

A NOR gate is the negation of the OR of its inputs. It outputs true only when every input is false because OR would be false when all inputs are false, and inverting that gives a true output. If any input is true, the OR result is true, and the NOR output becomes false. For two inputs, both false yields a true output; any true input yields a false output. This behavior matches the statement that outputs true only when all inputs are false. The other common gate behaviors—outputting true whenever any input is true (OR), outputs true only when all inputs are true (AND), or outputs true when at least one input is false (NAND in a broader sense)—do not describe NOR.