The correct answer is: A) The formation of modern Karnataka state.
Karnataka celebrates ‘Rajyotsava Day’ on November 1st to commemorate the formation of the modern Karnataka state on November 1, 1956. The state was formed by merging the Kannada-speaking regions of the erstwhile Bombay Presidency, Hyderabad State, Mysore State, and Coorg State.
Option B is incorrect because Karnataka was not victorious in any major battle.
Option C is incorrect because Karnataka Rajyotsava is not a cultural festival. It is a state holiday that commemorates the formation of the modern Karnataka state.
Option D is incorrect because Karnataka Rajyotsava is a celebration of the formation of the modern Karnataka state.