Five jumbled up sentences (labelled 1, 2, 3, 4 and 5), related to a topic, are given below. Four of them can be put together to form a coherent paragraph. Identify the odd sentence and key in the number of that sentence as your answer.

1. Boa Senior, who lived through the 2004 tsunami, the Japanese occupation and diseases brought by British settlers, was the last native of the island chain who was fluent in Bo.

2. The indigenous population has been steadily collapsing since the island chain was colonised by British settlers in 1858 and used for most of the following 100 years as a colonial penal colony.

3. Taking its name from a now-extinct tribe, Bo is one of the 10 Great Andamanese languages, which are thought to date back to pre-Neolithic human settlement of southeast Asia.

4. The last speaker of an ancient tribal language has died in the Andaman Islands, breaking a 65,000-year link to one of the world's oldest cultures.

5. Though the language has been closely studied by researchers of linguistic history, Boa Senior spent the last few years of her life unable to converse with anyone in her mother tongue.

The correct answer is 2.

To identify the odd sentence, let us analyze the thematic connections between the sentences to see which ones form a coherent paragraph:
- Sentence 4 introduces the core event: the death of the last speaker of an ancient tribal language in the Andaman Islands, which broke a 65,000-year cultural link.
- Sentence 3 follows up by identifying the specific language mentioned in Sentence 4, explaining that "Bo" is one of the 10 Great Andamanese languages and naming the now-extinct tribe it came from.
- Sentence 1 identifies the last fluent speaker of this language, "Boa Senior", and provides historical context about her life.
- Sentence 5 concludes the narrative about Boa Senior and the Bo language, highlighting the poignant detail that she spent her final years unable to speak to anyone in her mother tongue because there were no other speakers left.

Together, the sentences 4, 3, 1, and 5 form a logically ordered and coherent paragraph (4-3-1-5) focusing specifically on the death of Boa Senior and the extinction of the Bo language.

Sentence 2, while sharing the general context of British settlers in the Andaman Islands, shifts the focus to the demographic history and collapse of the entire indigenous population since 1858. It does not fit into the specific narrative flow concerning the extinction of the Bo language and its last speaker. Therefore, sentence 2 is the odd sentence.