Evil aliens have decided to kill everyone on Earth! Fortunately, they've given you two minutes to save as many as you can. All you have to do is name a country to save everyone in it.
In fact, the "elongated rectangle" hint is not very helpful, as there is a large number of flag in the 1:2 formats and other, which make them look "elongated" - thus, this shape is not really that unusual.
Sri Lanka should be removed. A flag with a ratio of 1:2 is not at all uncommon. However, flags with ratios shorter than 2:3 are uncommon, as others have mentioned.
Btw love the quiz.