The correct answer is: C. Tri-calcium aluminate
Tri-calcium aluminate (C3A) is the constituent of cement which is responsible for all the undesirable properties of cement. It is the most reactive of the four main cement minerals, and it is responsible for the early strength development of cement. However, it is also the most unstable mineral, and it is responsible for the expansion and cracking of concrete that is exposed to sulfates.
Di-calcium silicate (C2S) is the second most reactive of the four main cement minerals. It is responsible for the later strength development of cement. It is also less reactive than C3A, and it is not as susceptible to sulfate attack.
Tri-calcium silicate (C3S) is the most abundant of the four main cement minerals. It is responsible for the initial setting and hardening of cement. It is also less reactive than C3A, and it is not as susceptible to sulfate attack.
Tetra calcium alumino ferrite (C4AF) is the least reactive of the four main cement minerals. It is responsible for the long-term strength development of cement. It is also the most stable mineral, and it is not susceptible to sulfate attack.
In conclusion, tri-calcium aluminate (C3A) is the constituent of cement which is responsible for all the undesirable properties of cement. It is the most reactive of the four main cement minerals, and it is responsible for the early strength development of cement. However, it is also the most unstable mineral, and it is responsible for the expansion and cracking of concrete that is exposed to sulfates.