Explanation:

- Statehood Day of Tripura is observed on 21 January. This marks the day in 1972 when Tripura, along with Meghalaya and Manipur, became full-fledged states in India.

- 13 October: This date is not related to Tripura's statehood day. It does not hold significance in the context of the formation of the state.

- 2 March: This date is not relevant to Tripura's statehood. It might be associated with other events, but not linked to Tripura's statehood recognition.

- 21 January: This is the correct date for Tripura’s Statehood Day. On this day in 1972, Tripura transitioned from being a Union Territory to becoming a state of India.

- 21 February: This date is not linked to Tripura’s statehood day. It might be significant for other historical or cultural reasons but is not pertinent to this context.

- Correct Answer: Option 3 - 21 January