Indian fertilizer plants — A plant manufacturing ammonium sulphate by the gypsum–ammonia route (instead of the usual direct sulphuric acid neutralization) is located at which of the following sites?

Introduction:
Ammonium sulphate can be produced by several routes: neutralization of ammonia with sulphuric acid, recovery from coke-oven gas, caprolactam byproduct, or reaction of gypsum with ammonia and carbon dioxide. Historical plant locations in India reflect raw-material availability and integration with steel or chemical complexes.

Given Data / Assumptions:

• Question refers to the gypsum–ammonia process.
• Sites listed include steel-associated and fertilizer corporation locations.
• Historical context of public-sector plants.

Concept / Approach:
The gypsum–ammonia route converts CaSO4·2H2O with NH3 and CO2 (from calcination/limestone or other sources) into (NH4)2SO4 and CaCO3. In India, the Sindri unit of the Fertilizer Corporation of India (FCI) is classically associated with diversified fertilizer manufacture and has been cited with ammonium sulphate production including non-conventional routes.

Step-by-Step Solution:
Identify which option corresponds to an FCI fertilizer complex historically noted for AS production.Select Sindri (under FCI).Other sites are primarily steel or different chemical complexes not noted for the gypsum–ammonia route.

Verification / Alternative check:
Industry references on legacy Indian fertilizer plants attribute gypsum–ammonia AS manufacture to Sindri operations in specific periods, distinguishing it from caprolactam byproduct AS at Baroda (GSFC) or coke-oven recovery at steel plants.

Why Other Options Are Wrong:

• Rourkela/Bokaro: steel plants where AS would more likely be byproduct from coke-oven gas.
• Baroda (GSFC): associated with caprolactam byproduct AS, not gypsum–ammonia as the main route.
• Vizag: not the canonical example for the gypsum–ammonia AS route.

Common Pitfalls:
Assuming all AS is made by direct acid neutralization; overlooking historical process diversity tied to local feedstocks.

Final Answer:
Sindri (under FCI)