There are two possible answers to this question. I would suggest that you should check in your textbook or in your class notes to see which of these answers your instructor prefers. The two possibilities are Wales and Northern Ireland. Of the two, I would argue that Wales is the better answer.
The United Kingdom is made up of four countries. These countries are England, Scotland, Northern Ireland, and Wales. The UK also has a number of overseas possessions and crown dependencies. Crown dependencies include Guernsey, Jersey, and the Isle of Man. Overseas possessions are the remnants of the British Empire and include such places as Bermuda, the British Virgin Islands, and the Falkland Islands. These places are often forgotten about, but they are not technically part of the UK.
It is fairly common for people to forget that Northern Ireland is part of the UK. One reason is that it has a very small population. There are fewer than 2 million people living in Northern Ireland. Another reason is the fact that Northern Ireland is not on the same island as the rest of the UK. Instead, it is on the island of Ireland and has “Ireland” as part of its name. It is likely that many people simply think that it is a region of the Republic of Ireland.
However, it is likely that many people do know that Northern Ireland is part of the UK because of the political violence that has long occurred there. People are likely to know that unionists and republicans have been fighting over whether Northern Ireland should remain a part of the UK. Therefore, I would say it is not the most forgotten part of the UK.
I would say that Wales is the most forgotten part of the UK. Like Northern Ireland, it is rather small, with only about 3 million residents. It does not have a territory that is clearly distinct from that of England in the minds of most people. Unlike Scotland, it did not continue to fight to remain separate from England for a long time. This means that there are not movies like Braveheart to make Americans more aware of Wales. In short, there is not much that makes most people outside the UK think of Wales as a distinct part of the UK.
For these reasons, I would argue that Wales is the best answer to this question.
Wales or Northern Ireland