Exp) Option d is the correct answer.

Extra-constitutional measures are those devices which are not mentioned in the constitution. These extra-constitutional measures promote cooperation and coordination between the Centre and the states. These include a number of advisory bodies and conferences held at the Central level. Of the above given bodies, only 1, 3, 5 and 6 are correct. These bodies are NITI Aayog, National Integration Council, The Central council of Health and family welfare, The Zonal council, UGC (University Grants commission, The Governor’s conferences, The Chief minister’s conferences, The Chief secretaries’ conferences etc.

2 and 4 are incorrect. Inter-State council is not an extraconstitutional device as it is mentioned in Article 263 of the constitution. All India services is also mentioned in article 312 of the constitution and so it is not an extra-constitutional device. The members of these services occupy top positions (or key posts) under both the Centre and the states and serve them by turns.