What is the input impedance of a theoretically ideal op-amp?

A theoretically ideal operational amplifier is designed so that it draws absolutely no current from the signal source connected to its inputs. To achieve this, its input impedance must be infinitely high. In practical, real-world op-amps, the input impedance is not infinite, but it remains very high, often in the megaohm or gigaohm range. This exceptionally high input impedance ensures that the op-amp does not load down or alter the delicate input signals it is meant to measure and amplify. Choosing options like 'very low' or specific low values (like 100 or 1000 ohms) would result in a circuit that draws significant current, causing severe signal loss and distortion from the source.