Explanation:

- Option 1: 1968

- This is not the correct year for the renaming of Madras State to Tamil Nadu.

- Discussions and proposals for renaming were ongoing during this period.

- Option 2: 1971

- This year is not significant to the renaming event.

- Other political events happened around this time but unrelated to the renaming.

- Option 3: 1969

- The proposal was in discussion by then.

- However, this is not the correct year for the official renaming.

- Option 4: 1970

- Time for the important legislative changes in the state.

- The correct year for renaming Madras State to Tamil Nadu is indeed January 14, 1969!