Voltmeter is used to measure-
A) Current
B) Electric power
C) Potential difference
D) Consumption of energy

Hint
Voltmeter is a device in which a large resistance is connected in series with a galvanometer. Voltmeters always connect in parallel in circuits because its resistance is very large. Voltmeter tells us the voltage difference between two points in the circuit.

Complete step by step solution
Current is measured by ammeter which is connected in series with circuit and its resistance is very small. Voltmeter tells us the voltage difference between two points in the circuit. Means we can measure potential difference with voltmeter. To measure the potential difference, we always connect voltmeter in parallel with circuit and we connect voltmeter at the points between which we need to find potential difference.
Electric power measured using ammeter and voltmeter but not only using voltmeter.
consumption of energy is measured by an electric meter similar to the meter at our home.
Hence correct answer is option (C).

Note
We know that electric power is a product of potential difference and current flows through the circuit, then we measure power by using voltmeter but also need ammeter that’s why we didn’t calculate power by using only voltmeter.