Concept:Gypsum is added to cement to regulate its setting time, acting as a retarder to prevent flash setting.
Explanation:Setting time is the time required for cement paste to stiffen to a defined consistency.
Pure cement would set very quickly upon adding water, which is undesirable for construction.
Gypsum, with chemical formula
CaSO4​⋅2H2​O, is added during grinding.
It reacts with tricalcium aluminate (
C3​A) to form ettringite, which coats the cement particles and slows hydration.
This increases the setting time, allowing sufficient working time.
Thus, gypsum lowers the setting rate relative to cement without gypsum.
Answer:B. Gypsum