The year Karnataka (then Mysore State) was formed based on linguistic lines:

The correct answer is B) 1956.

Karnataka was formed on November 1, 1956, by merging the Kannada-speaking areas of the erstwhile Bombay Presidency, Hyderabad State, Mysore State, and Madras State. The formation of Karnataka was based on the linguistic reorganization of states that took place in India in 1956.

Option A) 1950 is incorrect because the States Reorganization Act, which led to the formation of Karnataka, was passed in 1956.

Option C) 1961 is incorrect because Karnataka was formed in 1956, not 1961.

Option D) 1973 is incorrect because Karnataka was formed in 1956, not 1973.