Explanation:

Chief Ministers of all the states are ex-officio members of:

- Planning Commission:

? This body was dissolved in 2014 and replaced by NITI Aayog. Even when it existed, all Chief Ministers weren’t ex-officio members—just a subset were invited.

- National Development Council (NDC):

? All Chief Ministers of states and Union Territories are ex-officio members here. The NDC was a bridge between the Centre and the states for discussing development plans.

- Inter State Council:

? Here’s the thing—Chief Ministers are indeed ex-officio members. This council is meant to discuss and resolve disputes or issues among states, with the Prime Minister as Chairperson.

- Finance Commission:

? This is a constitutional body. Chief Ministers are not members at all—the Finance Commission has its own appointed experts.

Correct Answer: Option 3, Inter State Council.