The correct answer is: b) 1975.
Sikkim became the 22nd state of India on May 16, 1975. It was previously an independent kingdom, but it was annexed by India in 1975. The annexation was controversial, but it was ultimately accepted by the Sikkimese people.
Sikkim is a small state in the Himalayas. It is bordered by Nepal to the west, Bhutan to the north, China to the east, and West Bengal to the south. The capital of Sikkim is Gangtok.
Sikkim is a beautiful state with a rich culture. It is a popular tourist destination, and it is known for its mountains, forests, and monasteries.
The options a), c), and d) are incorrect because Sikkim did not become the 22nd state of India in those years.