I have to use the clues given to solve the puzzle of which place they're talking about:

'This is the largest city of this island country. Big Ben is located here'

I think the country is Britain so...London?

Thanks
-MC

Also, what country has a capital that was once named after King Christian IV?

Thanks
-MC

Your first answer is right.

Check this site for your second answer.

http://en.wikipedia.org/wiki/History_of_Oslo

Yes, you are correct! The clues given, such as "this is the largest city of this island country" and "Big Ben is located here," can be used to deduce that the place being described is London, which is the capital city of the United Kingdom (UK). Big Ben is a famous landmark in London, and the UK is indeed an island country. Therefore, London is the correct answer. Well done!