The capital city of Karnataka state is

Explanation : When we discuss these options we can find that:

Chennai is the capital city of Tamil nadu.

Mysore is a city of karnataka. It has no capital.

Mangalore is a port city of karnataka

Capital city of Karnataka is Bengaluru (generally called Bangalore). It is a genuine district which was overseen by Western Ganga, the Chola and the Hoysala line. Bangalore is known as the electronic capital of India. Most of the information development is done in Bangalore.

Final Answer: Hence the correct option is D i.e. Bengaluru.