Explanation:

- Option 1: Patna

- Patna is the capital city of Bihar.

- It is not known for hosting the TISCO plant.

- Option 2: Darbhanga

- Darbhanga is a city in Bihar, known for its rich history.

- It does not house a major steel plant like TISCO.

- Option 3: Dhanbad

- Dhanbad, located in Jharkhand, is famous for coal mining activities.

- It is not the location of the TISCO plant.

- Option 4: Tatanagar

- Tatanagar, also known as Jamshedpur, is indeed where the TISCO plant is located.

- TISCO stands for Tata Iron and Steel Company, now Tata Steel.

- Jamshedpur is named after Jamshedji Tata, founder of Tata Steel.

Answer: Tatanagar