The correct answer is Hong Kong.
The island of Hong Kong was ceded to the British during the First Opium War with the signing of the Chuenpi Convention.
The First Opium War was a series of military engagements fought between the United Kingdom and the Quing dynasty in China over diplomatic relations, trade and administration of justice in China.
Excluding the Japanese occupation during the the Second World War, Hong Kong was under British rule from 1841 to 1997. The island was ceded by Quing China in the aftermath of the war and established as the Crown Colony in 1843.
The entire colony was transferred back to China in 1997.
