Answer : 3. "Cotton Textile Industry"
Explanation :

1. All the economic activities done for livelihood in which currencies are exchanged directly or indirectly are called industries.

2. The oldest and most organized industry of Rajasthan is cotton textiles.

3. The first cotton mill in India was established in 1818 at Dhusari, Calcutta, while the first cotton mill in Rajasthan was established in 1889 at Beawar, Ajmer, The Krishna Mills.

4. Bhilwara district in Rajasthan is the main centre of the cotton textile industry, hence it is called the Manchester of Rajasthan.