6 DO
Which are examples of a medium?
water and air
amplitude and wavelength
crests and troughs
compressions and rarefactions

water and air

Explanation:

The examples of medium from this problem is water and air.

A medium is an agency or a means of propagating energy, waves or even facilitating a chemical reaction.

Fluids are very good medium in chemistry for chemical reactions. The two most common media used are air and water.

In physics, a vacuum is an empty space that has been evacuated. It also serves as a medium to study some physical phenomenon.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)

yes the answer is total mass in unchanged   : )