AND and OR gates can have any number of inputs, but the most common are 2-input and 3-input gates. Larger gates with more than 3 inputs are also possible.

NAND and NOR gates are functionally equivalent to combining an AND/OR gate with a NOT gate. So a NAND gate produces a 1 output only if any input is 0, while a NOR gate outputs 1 only if all inputs are 0.

Yes, it is possible to construct any logic circuit using only NAND or NOR gates due to their functional completeness property. This is because both these universal gates can mimic the behavior of an AND, OR and NOT gate.

The XOR gate finds application in hash functions, error detection/correction codes and other places that require detecting differences between two signals. It is used in half adders as part of binary addition.

CMOS gates have high noise immunity, low power consumption, ease of manufacture and can be densely packed on chips compared to other logic families like TTL. This makes CMOS the most widely used semiconductor logic technology today.