Everything has mass. The mass of something never changes.
Mass is measured using grams.
Air is not that heavy, but it certainly has mass because it takes up space.
For every one liter of air, their is 1.19 grams.
Correct answer - Frequency.
Why? - The frequency, is the number of waves that pass a certain point in a specified amount of time.
Transport
The protein is working to transport substances across the membrane.