Your question is slightly wrong. The United Kingdom is comprised of England, Scotland, Wales and Northern Ireland. The island of Ireland is divided. Most of the island is occupied by the Republic of Ireland but there are six counties of the province of Ulster which is in the northeast corner of the island, which are part of the United Kingdom.
No it is an island (the island of Ireland or Eire). The island is divided into two parts the Republic of Ireland, and Northern Ireland which is a part of the United Kingdom.
The United Kingdom is England, Wales, Scotland, and Northern Ireland.
The UK was divided into four parts, them being England, Scotland, Wales and Northern Ireland.
Northern Ireland is one of the four parts of the United Kingdom.
The 'united kingdom' is properly styled The United Kingdom of Great Britain and Northern Ireland. It comprises England and Wales Scotland Northern Ireland England, Scotland and Northern Ireland are distinct and separate parts. Wales is a principality.
Boroughs. There are many Boroughs of London, such as Islington, Hounslow, Westminster.
England, Scotland and Wales. Northern Ireland is on the island of Ireland.
The United Kingdom consists of England, Scotland, Wales and Northern Ireland.
There is no UK mainland. The United Kingdom consists of England, Scotland, Wales and Northern Ireland. Without any of those 4 parts, it is not the United Kingdom. England, Scotland and Wales are on the island often called Britain, whereas Northern Ireland is on the island of Ireland. So Northern Ireland is not in Britain, but it is in the United Kingdom. This is what you are confusing.
There is no such thing as the United Kingdom of America. There is the United States of America (USA) which has 50 states. The United Kingdom of Great Britain and Northern Ireland (UK) is a completely separate country which has 4 parts (England, Scotland, Wales and Northern Ireland).
The United Kingdom (UK) is a constitutional monarchy and unitary state consisting of four countries; England, Northerin Ireland, Scotland and Wales.
The island of Ireland is shared between the Republic of Ireland and six counties in the northeast of the island which is referred to as Northern Ireland and is part of the United Kingdom.