21. Which of the following will have the largest interfacial area per unit volume?
A. A bubble with a diameter of 1 mm
B. A bubble with a diameter of 5 mm
C. A bubble with a diameter of 15 mm
D. A bubble with a diameter of 50 mm
22. Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft?
A. Anemometer
B. Manometer
C. Tachometer
D. Barometer