Which instrument is used to measure the power of electric circuit ?

A. Wavemeter
B. Viscometer
C. Wattmeter
D. None of these

A wattmeter is an electrical instrument which is used to measure the electric power (in watts) of any electrical circuit.
Voltmeter – is used to measure electric potential difference between two points,
Wavemeter – is used to measure the wavelength of a radiowave,
Viscometer – is used measure viscosity of liquid.