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

## Step 1<br />In the context of physics, a medium is defined as a material or space through which waves can travel. This can include a variety of substances, such as water, air, or even a vacuum.<br /><br />## Step 2<br />The options provided in the question are: water and air, amplitude and wavelength, crests and troughs, and compressions and rarefactions.<br /><br />## Step 3<br />Among these options, water and air are examples of a medium because they are substances through which waves can travel.<br /><br />## Step 4<br />On the other hand, amplitude and wavelength, crests and troughs, and compressions and rarefactions are not examples of a medium. They are terms used to describe different aspects of waves, not the medium through which the waves travel.