why does mount not appear in utilities

In Terminal execute this command to see usage...

man mount

In DU is there an Unmount button, if so that means the highlighted drive or partition on the left is mounted, that same button will change toMount.

As in mount for drives?

It should be automatic, but there is a Mount in Disk Utility & a mount in Terminal.

Try Option+CMD+t keys to Show Toolbar...

Grayed out or not showing at all?