Question

Which of the following logic gates is a universal gate?

• A. OR
• B. NOT
• C. AND
• D. NAND

Answer 1

Answer: (D)

The $NAND$ gate and the $NOR$ gate can be said to be universal gates since combinations of them can be used to accomplish any of the basic operations and can thus, produce and inverter, an $OR$ gate or an $AND$ gate. The non-inverting gates do not have this versatility since they can't produce an invert.
The basic symbol and truth table of $NAND$ gate are shown.