Explanation:

- National Unity Day (Rashtriya Ekta Diwas) is observed in India to commemorate the birth anniversary of Sardar Vallabhbhai Patel, the first Deputy Prime Minister and Home Minister of India.

- Sardar Patel is remembered for his role in unifying the country after independence.

 October 31 is the correct date for National Unity Day. It marks Patel's birth anniversary and was first celebrated in 2014.

- The other options (October 30, October 28, October 29) are incorrect.

- October 30, 28, and 29 do not hold any significance related to National Unity Day.

- The observance promotes the spirit of unity and integrity among Indians.