Portland cement contains ${}^{\prime }{X}^{\prime }$ to enhance the setting time. What is ${}^{\prime }{X}^{\prime }$?

1. $CaS{O}_4\cdot \frac{1}{2}{H}_{2}O$
2. $CaS{O}_4\cdot 2H_{2}O$
3. $CaC{O}_3$
4. $CaS{O}_4$

The correct option is B $CaS{O}_4\cdot 2H_{2}O$
Gypsum is added in portland cement to slow down the process of setting of the cement so that it gets sufficient time to hardened.