Addition of gypsum to cement:A. reduces setting time of cementB. produces very light colour cementC. increases setting time of cementD. shining surface is formed

The correct answer is C. increases setting time of cement.

Explanation:
Gypsum (CaSO₄·2H₂O) is added to cement primarily to control the setting time. When water is mixed with cement, a chemical reaction called hydration occurs, which leads to the hardening of cement. Without gypsum, this reaction would happen too quickly, causing the cement to set prematurely (flash setting), which is not desirable in construction as it would make working with the cement difficult.

Gypsum slows down the reaction of tricalcium aluminate (C₃A) with water, thus increasing the setting time of cement. This allows the cement to be workable for a longer period before it hardens.

Other Options:
A. reduces setting time of cement: Incorrect. Gypsum increases, not reduces, the setting time.
B. produces very light colour cement: Incorrect. Gypsum does not affect the color of the cement significantly.
D. shining surface is formed: Incorrect. Gypsum does not form a shiny surface on cement.
Hence, the correct answer is C.