The correct answer is Assam.

• Digboi Oil Refinery, commissioned on 11th December 1901, is India's oldest operating refinery and one of the oldest operating refineries in the world. It is located in Assam.

Assam

• Kamarupa is the old name of Assam.
• Dispur is the capital of Assam.
• Assam is known as the 'Tea Garden of India'.
• Assam is the leading producer of tea in India.
• Assam is known as the 'Gateway to the North Eastern States of India'.
• Assam shares international boundaries with Bhutan and Bangladesh.
• Guwahati is known as the 'light of the east'.
• Guwahati High court is the largest jurisdiction in terms of states (4 states).
• Jorhat is the cultural capital of Assam.
• The Brahmaputra is known as Sorrow of Assam.
• Manas National Park is famous for Royal Bengal Tigers.
• Kaziranga National Park is famous for its one-horned rhinoceros.
• Orang National Park is known as the Mini Kaziranga.
• Dibru Saikhova in Assam is the smallest biosphere reserve in India.
• Majuli Island is the biggest riverine island in the world is situated in the river Brahmaputra.

• Bhupen Hazarika Bridge or Dhola Sadiya bridge is the longest bridge in India, over the River Lohit, in Assam.

Gujarat

• Gandhinagar is the capital of Gujarat.
• Gujarat is known as 'the Land of Legends'.
• Gujarat has the longest coastline in India.
• Kandla is the first Special Economic Zone in India.
• The first four-lane Express Highway in India was established in Gujarat (Ahmedabad to Vadodara). It is known as National Expressway 1 or MahatmaGandhi Expressway 1.
• Largest Oil Refinery in India - Jamnagar Oil Refinery (Reliance).
• The Gir National Park in Gujarat is famous for Asiatic Lions.
• Ran of Kutch is the largest biosphere in India
• The tallest statue in the world - Sardar Vallabhai Patel (182 meters) known as the Statue of Unity in Vadodara on the banks of the Narmada river in Gujarat.
• The first Railway Univesity in India is in Vadodara.
• Judicial Capital of Gujarat - Ahmedabad

Odisha

• The old name of Odhisa was Kalinga.
• The tagline of Odhisa is "The soul of Incredible India".
• Bhubaneswar is the capital of Odhisa and known as the 'Temple city' and 'Cathedral city of India'.
• Rourkela is the industrial capital of Odhisa.
• Cuttack is the cultural capital of Odhisa.
• The high court of Odhisa is situated in Cuttack
• Konark Sun Temple is known as 'Black Pagoda' is at Odhisa.
• Jaganatha Temple is situated at Puri in Odhisa.
• Chilka Lake is the largest saline water lake in India.
• Hirakud is the longest dam in the world built across the Mahanadi river.
• The Mahanadi is known as Sorrow of Odhisa.
• Nandankanan Tiger Reserve is famous for White Tigers.
• Paradip is the major seaport of Odhisa.

Uttar Pradesh

• Lucknow is the capital of Uttar Pradesh.
• Uttar Pradesh is the most populous state in India.
• Uttar Pradesh is the 'Sugar Bowl of India'.
• Uttar Pradesh has the largest number of monuments in India.
• Uttar Pradesh has the maximum membership (80 seats) in the Lok Sabha.
• Uttar Pradesh shares its boundary with the most number of states in India (9 states - Rajasthan, Haryana, Himachal Pradesh, Delhi, Uttarakhand, Bihar, Madhya Pradesh, Jharkhand, and Chhattisgarh including Delhi and Nepal).
• Asia's first DNA bank is in Lucknow in Uttar Pradesh.
• Uttar Pradesh is the state through which most numbers of the National Highways pass.