What instrument is used to measure resistance?

An ohmmeter is specifically designed to measure electrical resistance in a circuit or component. It works by applying a small voltage across the resistance and measuring the current that flows through it. By using Ohm's law (V = I x R), the device calculates the resistance based on the voltage applied and the current measured.

In contrast, an oscilloscope is used to visualize electrical signals as waveforms, which helps in analyzing voltage over time but does not measure resistance directly. A spectrum analyzer analyzes the frequency spectrum of signals, focusing on how signal power is distributed with frequency, which also does not measure resistance. A noise bridge is utilized primarily in radio frequency applications to measure impedance, focusing specifically on matching and tuning rather than measuring resistance alone.

This specificity of the ohmmeter in measuring resistance makes it the correct choice for this question.