Concept:
NITI Aayog is a major policy-making institution of the Government of India.
Step 1:
NITI Aayog stands for National Institution for Transforming India.
Step 2:
It was established on 1 January 2015 by the Government of India.
Step 3:
NITI Aayog replaced the Planning Commission, which was responsible for centralized economic planning.
Step 4:
The new institution was created to promote cooperative federalism and policy innovation.
Step 5:
Therefore, the correct answer is Planning Commission.
\[
\boxed{\text{(3) Planning Commission}}
\]