What was the nature of the Planning Commission as an institution?

The correct answer is Option 4 - Extra-constitutional and non-statutory

The Planning Commission was set up in March 1950 by a simple resolution of the Government of India. The Prime Minister was its Chairperson. It was an extra-constitutional and non-statutory body. It became the most influential & central machinery for deciding what path & strategy India would adopt for its development. It had an advisory role and its recommendations became effective only when the Union Cabinet approved these.