Question

Which of following are known as universal gates?

• A. \( \text{NAND and NOR} \)
• B. \( \text{AND and OR} \)
• C. \( \text{XOR and OR} \)
• D. \( \text{AND} \)

Hint:

Remember that NAND and NOR gates are called "universal" because any digital circuit or Boolean expression can be realized using only NAND gates or only NOR gates. This property is fundamental in digital circuit design.

Answer 1

The Correct Option is A

Step 1: Understand the definition of universal gates. Universal gates are logic gates that can be used, either individually or in combination, to implement any other basic logic gate (AND, OR, NOT) or any Boolean function. Step 2: Identify the standard universal gates. In digital logic, the NAND gate and the NOR gate are known as universal gates. \begin{itemize} \item Using only NAND gates, one can construct AND, OR, and NOT gates. \item Similarly, using only NOR gates, one can also construct AND, OR, and NOT gates. \end{itemize} Step 3: Evaluate the given options based on this definition. \begin{itemize} \item (a) NAND and NOR: Both are recognized as universal gates. \item (b) AND and OR: These are basic gates but not universal. For example, you cannot create a NOT gate using only AND or only OR gates. \item (c) XOR and OR: Neither XOR nor OR is a universal gate. \item (d) AND: AND is a basic gate, not universal. \end{itemize} Step 4: Conclude that NAND and NOR gates are the universal gates. Therefore, option (a) is the correct answer.