Which channel separates mainland Scotland from the Orkney Islands?

The Pentland Firth separates mainland Scotland from the Orkney Islands.

It is a strait in northern Scotland between Caithness on the mainland and the southern Orkney islands. The passage links the North Atlantic and the North Sea and is known for exceptionally strong tidal currents. At its western end, the firth opens toward the waters around the Scottish mainland; at its eastern end, it leads toward the North Sea.

The Pentland Firth has become an important location for testing tidal-energy technology because predictable currents flow through its narrow channels. The tidal race near the islands can create powerful whirlpools and turbulent water. It is distinct from the Minch, the larger sea area west of mainland Scotland and the Outer Hebrides, and from the North Channel between Scotland and Northern Ireland.