A sector that has seen significant liberalization in Tamil Nadu is:

Retail
Agriculture
Power
Textiles

The correct answer is: Retail.

Tamil Nadu has seen significant liberalization in the retail sector in recent years. The state government has taken steps to promote private investment in the sector, including by simplifying the process of obtaining licenses and permits. As a result, the number of retail outlets in the state has increased significantly, and consumers have benefited from a wider range of goods and services at lower prices.

The agriculture sector is another sector that has seen some liberalization in Tamil Nadu. The state government has taken steps to reduce the role of the government in the sector, including by privatizing some agricultural cooperatives. However, the sector remains heavily regulated, and there is still a long way to go before it can be considered truly liberalized.

The power sector is another sector that has seen some liberalization in Tamil Nadu. The state government has taken steps to attract private investment in the sector, including by privatizing some state-owned power companies. However, the sector remains heavily regulated, and there is still a long way to go before it can be considered truly liberalized.

The textiles sector is another sector that has seen some liberalization in Tamil Nadu. The state government has taken steps to promote private investment in the sector, including by providing tax breaks and other incentives. However, the sector remains heavily regulated, and there is still a long way to go before it can be considered truly liberalized.

In conclusion, the retail sector is the sector that has seen the most significant liberalization in Tamil Nadu. The state government has taken steps to promote private investment in the sector, and as a result, the number of retail outlets in the state has increased significantly, and consumers have benefited from a wider range of goods and services at lower prices.