There are two mountainous members of the United Kingdom.
So, the answer you are looking for is Wales.
Scotland and Wales
Ireland.
Ireland is the smallest country in the British Isles
The relief of the british isles is how the hight varies e.g. low land and high land. You can find the relief of the british isles mainly in an atlas colour coded to help you e.g. purple = mountainous and green = flat land.
Ireland is the closest country to the British Isles. It is located just to the west of Great Britain.
Scotland.
England.
The Republic of Ireland is geographically part of the British Isles.
Wales is not an independent nation; it is part of the United Kingdom along with England, Scotland, and Northern Ireland.
England is a country, it can be found in the British Isles
That would be Iceland.
Wales