Which of the following is an universal gate ?

A universal gate is a logic gate that can be used to implement any Boolean function without needing any other type of gate. Among the options provided, only the NOR gate and NAND gate possess this property. The NOR gate is universal because it can be combined to create the basic logic functions: NOT, AND, and OR. For instance, connecting both inputs of a NOR gate together creates a NOT gate, while combining multiple NOR gates allows the construction of AND and OR gates. In contrast, the AND gate (Option A) cannot produce a NOT function on its own without an inverter. Similarly, the OR gate (Option B) cannot generate a NOT function independently. The XOR gate (Option D) is also not universal because it cannot implement all basic logic functions like AND or OR without additional components. Therefore, since the NOR gate can replicate any other basic logic gate configuration, it is classified as a universal gate.