The correct answer is option 'D' - 14th November. Let's discuss each of the given options to understand why it is not a national holiday.

a) 15th August
- 15th August is celebrated as Independence Day in India. It is a national holiday and marks the day when India gained independence from British rule in 1947. This day is observed with flag hoisting ceremonies, cultural programs, and various other festivities throughout the country.

b) 26th January
- 26th January is celebrated as Republic Day in India. It is a national holiday and commemorates the day when the Constitution of India was adopted in 1950, making India a sovereign, socialist, secular, and democratic republic. The celebrations include a grand parade in the capital city, New Delhi, showcasing the country's cultural diversity and military strength.

c) 2nd October
- 2nd October is celebrated as Gandhi Jayanti in India. It is a national holiday and honors the birth anniversary of Mahatma Gandhi, the Father of the Nation. On this day, various events and programs are organized to pay tribute to Gandhi's ideals of non-violence, peace, and harmony.

d) 14th November
- 14th November is not a national holiday in India. However, it is celebrated as Children's Day, also known as Bal Diwas, in India. This day marks the birth anniversary of Pandit Jawaharlal Nehru, the first Prime Minister of India, who was fondly called Chacha Nehru (Uncle Nehru) by children. Schools and educational institutions often organize special activities, cultural programs, and competitions for children on this day.

In conclusion, among the given options, 14th November (option 'D') is not a national holiday in India. Instead, it is celebrated as Children's Day to honor the birth anniversary of Pandit Jawaharlal Nehru.