The correct answer is A. PH meter.
A pH meter is a device used to measure the pH (acidity or alkalinity) of a solution. It is a handheld device with a probe that is inserted into the solution. The probe contains a sensor that measures the concentration of hydrogen ions in the solution. The pH meter then displays the pH value on a digital display.
An ammeter is a device used to measure the current in an electrical circuit. It is a small, handheld device with two terminals. The terminals are connected to the circuit, and the ammeter measures the current flowing through the circuit.
A hygrometer is a device used to measure the humidity of the air. It is a small, handheld device with a sensor that measures the amount of water vapor in the air. The hygrometer then displays the humidity level on a digital display.
An acidmeter is a device used to measure the acidity of a solution. It is a small, handheld device with a probe that is inserted into the solution. The probe contains a sensor that measures the concentration of hydrogen ions in the solution. The acidmeter then displays the acidity level on a digital display.
The pH meter is the most accurate device for measuring the acidity of a solution. The ammeter, hygrometer, and acidmeter are not as accurate for measuring acidity.