In which year was the erstwhile Mysore State renamed as Karnataka?

1973

The correct answer is Option (3) → 1973

The erstwhile Mysore State was renamed as Karnataka in 1973.

The renaming took place officially on November 1, 1973, under the leadership of then Chief Minister D. Devaraj Urs. This change occurred exactly 17 years after the state was originally unified and formed on linguistic lines as "Mysore State" in 1956.