Fill in the blanks with the most appropriate option:-

He can speak Marathi ___________ he was born in Uttar Pradesh.

although

The most appropriate option to fill in the blanks is although.

The word "although" is a conjunction that introduces a contrast. In the context of the sentence, "He can speak Marathi although he was born in Uttar Pradesh", the fact that he can speak Marathi contrasts with the fact that he was born in Uttar Pradesh. The other options are not as appropriate.

• So means for that reason. This does not make sense in the context of the sentence, as the fact that he can speak Marathi is not a reason for the fact that he was born in Uttar Pradesh.
• Because means on account of the fact that. This is the most appropriate word to use in the sentence, but it is not the most concise.
• So that means in order to. This does not make sense in the context of the sentence, as he does not need to be able to speak Marathi in order to have been born in Uttar Pradesh.