The correct answer is B. Ammeter.
An ammeter is an instrument used to measure electric current in a circuit. It is connected in series with the circuit, and the current flowing through the ammeter is proportional to the deflection of the needle on the ammeter’s scale.
A voltmeter is an instrument used to measure electric potential difference, also known as voltage. It is connected in parallel with the circuit, and the voltage across the voltmeter is proportional to the reading on the voltmeter’s scale.
A barometer is an instrument used to measure atmospheric pressure. It is typically a glass tube filled with mercury, which is open at one end and closed at the other. The mercury in the tube rises or falls in response to changes in atmospheric pressure.
A sinometer is an instrument used to measure the sine of an angle. It is typically a device with a graduated scale and a pointer that moves along the scale in response to the angle of rotation of a shaft.
I hope this helps!