The correct answer is option 4: a non-statutory body. Non-statutory bodies are institutions or organizations that are not established by an act of Parliament or a law. Instead, they are created by a government order or executive decision. In the case of the Planning Commission of India, it was formed through a government resolution in 1950. The Planning Commission was responsible for formulating and implementing economic plans for the country. However, it was replaced by the NITI Aayog in 2015, which is also a non-statutory body. Non-statutory bodies have less power and authority compared to constitutional, independent and autonomous, or statutory bodies. Therefore, option 4 is the correct choice.