Good quiz. The fact that I crossed the UK/Spanish border this afternoon helped to ensure that I got that one right. I've just one quible: You claim Saudi and Bahrain have a border - but it's on an artificial island. That's surely the same as suggesting that an artificial causeway or a bridge constitutes a border. Anything artificial should not count in a proper Geography quiz, just as a reservoir would not count as a lake.
In my opinion, an artificial island is completely different than a causeway or bridge since roads are not necessarily land and do not extend a country's maritime borders, while artificial islands are and do. That's the reason China is building islands in the South China Sea. Land is land whether it's manmade or natural and Passport Island even has around ten inhabitants which I would argue qualifies it as a piece of both Bahrain and Saudi Arabia. This, in turn, makes the two countries share a border on the island. By your logic, the Netherlands would lose 970 square kilometres because of its artificial island of Flevopolder. I'm not sure how the hundreds of thousands of inhabitants would feel about not technically living in their own country.
Great that you liked the quiz though! Thanks for the feedback
British Overseas Territories, according to their wikipedia page, "do not form part of the UK". This agrees with JetPunk quizzes in general where the UK isn't considered to include Gibraltar. Would be helpful if you added a caveat saying that you're including overseas territories. Good quiz though. Nice pick of countries :)
Great that you liked the quiz though! Thanks for the feedback