Question

The logic gates giving output ‘1’ for the inputs of ‘1’ and ‘0’ are
A. AND and OR
B. OR and NOR
C. NAND and NOR
D. NAND and OR
E. AND and NOR

Answer 1

Logic gates are idealized digital or electronic devices implementing a Boolean function. It has two or more inputs and on the basis of Boolean function implemented it produces a single output.
These are basically a representation of Boolean operations and functions-
On that basis they are of 7 types viz- AND, OR, XOR, NAND, NOR, XNOR and NOT.
They take two kinds of input, either 1 or 0, which in electronic form means ON and OFF respectively.
1 stands for ON or TRUE
0 stands for OFF or FALSE.
In the given question, the output is 1 and inputs are 0 and 1. To solve the question, as to which gate will produce such a result, we’ll need to know the possible results obtained through all these 7 gates via their truth tables.
*Truth tables are used to represent a Boolean expression in logic gates.

Complete step by step solution:
Let’s first construct the truth tables for all the gates for the given input 0 and 1.

1. AND gate – In this logic gate, for the output to be true both the inputs should be true. If any or all of them is false, then the output turns out to be false.
Truth table-
Let there be two inputs A and B respectively and let the output be O.

In AND gate, for the given input 0 and 1, the output is 0.

2. OR gate- In this logic gate, the output is true, when one or more than one inputs are true.
The truth table is shown below-

You see, for the given input 0 and 1, this gate yields the output 1, as is required in the question. So, this is one of the two gates.
Let’s check for other gates too-

3. NOT gate- It is the logic gate which takes one input and gives only one output. When the input of the NOT gate is true, then the output will be false and vice-versa.
Since, we are dealing with a gate which takes two inputs so this gate is out of question.

4. NAND gate- It is the logic gate made from the combination of AND and NOT gate.
It is basically the reverse of AND gate, so if the results of AND gate is true, then the output of NAND will be false and vice versa.
Truth table-

We see that for the given inputs this gate produces the output as we require in accordance with the question at hand.
Thus, for the input 0 and 1, the output we get is 1.

$\therefore$OR and NAND gate are the ones most suitable to be selected.

So, option D is the correct answer.

Note: To solve such a question, it’s not necessary to draw the truth table of all the 7 gates.
Just keep in mind the output that is obtained from them and if it’s a multiple-choice question, then only consider drawing the truth tables of the gates given in options to save time.
Point to keep in mind- NAND gate is the exact opposite of AND.
NOR gate is the exact opposite of OR.
So, if the output of AND is true, then for the same set of inputs, the output of NAND will be false.
Same holds true for NOR gate.