Question

NAND and NOR gates are called universal gates primarily because they
A) are available universally
B) can be combined to produce OR, AND, and NOT gates
C)are widely used in the integrated circuit package
D)are easiest to manufacture

Answer 1

Hint: Logic gates are used to do the mathematical operations by the IC’s. There are seven types of gates. Such as AND, OR, NOT, NAND, NOR, EX-OR, and EX-NOR. Out of these seven gates, NAND and NOR gates can act as universal gates.

Complete step by step answer:
The NAND and NOR gates can perform all the other operations of the gates such as logical AND, OR, and NOT gates.
The following figure shows the input output relation in NAND and NOR gates.

(i) NOR gates can be converted into the NOT gate by just connecting the inputs of a NOR gate. As a NOR gate is equivalent to an OR gate leading to NOT gate, this is automatically seen to the OR part of the NOR gate, eliminating it from consideration and leaving only the NOT part.
(ii) To convert the NOR into the OR gate, connect by just connecting the NOT gate followed to the NOR gate. As a result, outputs of this gate are opposite to that of the OR gate when the inputs are kept the same.
(iii) An AND gate gives the output as 1 when both of its inputs are 1. Therefore, an AND gate is made by inverting the inputs of a NOR gate.
(iv) A NAND gate can be converted into the NOT gate, by just connecting the inputs of NAND gates together.
(v) Not only AND, OR, and NOT gates, we can also combine the NAND gates to perform the EX-OR and NOR operations too.
An example of X-OR gate construction using NAND gates is shown below:

(vi) To construct each logic gate, we need specific IC’s. For example, to construct the AND gate we need IC 7408. But if we have the IC 7400 which is used to construct the NAND gate, we can form any logic gate using that single type of IC. The same goes for the NOR gate too.

$\therefore $ NAND and NOR gates are called universal gates because they can be combined to produce any of the other gates like OR, AND, and NOT gates. Hence the correct option is option (B).

Note:
AND and NOR gates can be suitable for all the options in the question. But the answer to why it is called universal gates means the only option is option B. NAND and NOR are economical and it is commonly used in many integrated circuit packages.