In Indian industrial and economic geography, this question asks you to identify which city is popularly known as the "Manchester of South India" because of its strong textile and cotton based industry.

Introduction / Context:
The nickname "Manchester" is often used in India for cities that are prominent textile and cotton industry centres, drawing a parallel with Manchester in the United Kingdom. In northern India, Ahmedabad is called the Manchester of the East. In southern India, another city has earned a similar nickname due to its concentration of textile mills and related industrial activity. This question checks whether you can correctly match that nickname with the city.

Given Data / Assumptions:
The question asks about the "Manchester of South India".
The options are Coimbatore, Salem, Thanjavur, and Madurai, all cities in Tamil Nadu.
We assume the nickname is based on the strength of the textile industry and cotton trade.

Concept / Approach:
Coimbatore is widely known as a major textile and engineering hub in South India. It has numerous spinning mills, textile factories, and related small scale industries, which has led to its popular nickname as the Manchester of South India. While Salem, Thanjavur, and Madurai are important in their own ways, they do not share this specific widely used nickname in standard GK references.

Step-by-Step Solution:
Step 1: Recall which southern city is most associated with the textile industry on a large scale. Step 2: Identify Coimbatore as a city that hosts many spinning mills, textile units, and engineering firms tied to this sector. Step 3: Compare this with Salem, Thanjavur, and Madurai, which are known for other features such as temples, agriculture, and regional trade. Step 4: Recognise that GK textbooks specifically describe Coimbatore as the "Manchester of South India". Step 5: Select Coimbatore as the correct answer.

Verification / Alternative check:
Geography textbooks and competitive exam guides state that Coimbatore, located in western Tamil Nadu, is a major centre of the textile industry, supported by favourable climate and cotton growing areas nearby. The city's economic profile and historical development around textile mills confirm why the comparison with Manchester is made. These same sources rarely, if ever, use this nickname for Salem, Thanjavur, or Madurai.

Why Other Options Are Wrong:
Salem: Known for steel plant operations and mangoes, among other things, but not widely called the Manchester of South India.
Thanjavur: Famous for its temples, art, and classical music heritage more than for large scale textile milling.
Madurai: Known for the Meenakshi temple and as a cultural and trading centre, but again not associated with this specific industrial nickname.

Common Pitfalls:
Aspirants sometimes mix up Manchester style nicknames and confuse Ahmedabad for this title in a question that is clearly about South India. Others guess among Tamil Nadu cities without recalling the industrial details. It is helpful to memorise both nicknames together: Ahmedabad as the Manchester of the East and Coimbatore as the Manchester of South India, so you can differentiate them clearly in exams.

Final Answer:
The city known as the "Manchester of South India" is Coimbatore.