By which Constitutional Amendment Act, Sikkim was made a full fledged state of the Indian Union?

By which Constitutional Amendment Act, Sikkim was made a full fledged state of the Indian Union?

किस संविधान संशोधन अधिनियम द्वारा सिक्किम को भारतीय संघ का पूर्ण राज्य बनाया गया था?

Topic : Sikkim GK