The correct answer is: a) Establish a democratic system in Sikkim.
The Praja Mandal movement was a political movement in Sikkim that aimed to establish a democratic system in the country. The movement was started in the early 20th century by a group of young Sikkimese people who were inspired by the Indian independence movement. The movement was successful in achieving its goal, and Sikkim became a democratic country in 1975.
Option b) is incorrect because the Praja Mandal movement did not seek religious freedom. The movement was secular in nature, and it did not advocate for any particular religion.
Option c) is incorrect because the Praja Mandal movement did not overthrow the British. The movement was a peaceful one, and it did not resort to violence.
Option d) is incorrect because the Praja Mandal movement did not aim to merge Sikkim with Nepal. The movement was focused on establishing a democratic system in Sikkim, and it did not have any plans to merge the country with Nepal.