Question

Why AND, OR, & NOT gate are called basic gates

Answer 1

AND OR NOT are basic gates because the other gates Nand,Nor,Ex-Or are works in the basis of those three basic gates
i.e. And + Not = Nand
Or + Not = Nor
Ex-Or is a exclusive-Or gate

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Answer 2

The AND, OR and NOT gate are considered as the basic gate since we form the basic circuit with the help of these gates only.

Then furthermore, the more gates are formed with the help of these basics only such as XOR, NOR, NAND and even XNOR.

Hence, they are considered as basic blocks.