The correct answer is option 1, 31st December, 1929. On this particular date, Jawaharlal Nehru unfurled the national flag of India on the banks of the Ravi river, as the clock struck midnight. This event is significant because it marked the launch of the Civil Disobedience Movement, which was a major step towards India`s independence struggle against British rule.

Let`s dissect the other options to understand why they are incorrect:

- Option 2: 26th January, 1930 - This date is significant because it is celebrated as India`s Republic Day, when the Constitution of India came into effect. However, it is not the date when Nehru unfurled the flag on the banks of the Ravi river.

- Option 3: 31st December, 1931 - This date has no significant record of Jawaharlal Nehru unfurling the flag on the banks of the Ravi river. It is not associated with any major historical event in India`s independence struggle.

- Option 4: 26th January, 1933 - This date also has no record of Nehru unfurling the flag on the banks of the Ravi river. It is not associated with any