Explanation: An ohmmeter is the correct instrument for measuring electrical resistance. Resistance, measured in ohms, is the opposition a material offers to the flow of electric current. In amateur radio, understanding resistance is crucial for circuit design, impedance matching, and troubleshooting components like resistors, wires, and antennas. * **A wattmeter** measures electrical power, typically in watts, which is the rate at which electrical energy is consumed or produced. This is vital for checking transmitter output. * **An ammeter** measures electric current, in amperes, which is the rate of charge flow through a circuit. It's used to monitor current draw in power supplies or amplifiers. * **A voltmeter** measures electrical potential difference, or voltage, in volts. This is used to check power supply levels or signal strengths.