Detailed Solution:

The correct answer is “1988”.

Uttarakhand is home to two UNESCO World Heritage Sites: the Nanda Devi and Valley of Flowers National Parks. The Nanda Devi National Park, located around the peak of Nanda Devi, is one of India's largest biosphere reserves and was declared a World Heritage Site in 1988. The Valley of Flowers National Park, also in the Garhwal Himalayas, was added to the list in 2005