Option 1 is incorrect because "residuary powers" under the Indian Constitution do not specifically relate to international affairs. Option 2 is also incorrect because it refers to powers in the context of an internal emergency, which is not the meaning of "residuary powers". Option 3 is incorrect because residuary powers do not necessarily include powers that can be exercised by both the Union Government and the States.

The correct answer is option 4. Residuary powers refer to the powers that have not been specifically listed or mentioned in the Union List, State List, or Concurrent List of the Indian Constitution. These are powers that do not fall within the jurisdiction of either the Union Government or the State Governments. Instead, they are retained by the central authority as residual or residual powers.