The correct option is C Arunachal Pradesh
India is the second most populated country in the world. According to the United Nations in July 2016, the population stood at 1.3 Billion. Population Density of India is 364 per sq km as per census 2011. Most of the North-eastern states are very least densely populated with Arunachal Pradesh being the least densely populated state with 16.5 population density per square km. while Mizoram is second with 51.8 population density per square km and Jammu & Kashmir and Sikkim are at 3rd and 4th respectively. Hence option C is correct.