Under Article 355 of the Constitution of India, it is the duty of the Union to :

 a) protect States against external aggression and internal disturbances.
 b) allow the extension of executive powers of the Union to any state.
 c) declare that the powers of the legislature pf a State shall be exercisable by or under the authority of the Parliament.
 d) allow the Parlaiment to include or exclude any caste, race or tribe int o the list of the Scheduled castes or Scheduled tribes.

CAPF 2015

Option (a)