The correct answer is: A. Tri-calcium silicate.
Tri-calcium silicate (C3S) is the most abundant mineral in Portland cement, accounting for about 60% of its weight. It is the main contributor to the strength of cement, and it is also responsible for the setting and hardening of cement
paste.Di-calcium silicate (C2S) is the second most abundant mineral in Portland cement, accounting for about 25% of its weight. It is also a contributor to the strength of cement, but it is not as important as C3S.
Tri-calcium aluminate
(C3A) is the third most abundant mineral in Portland cement, accounting for about 8% of its weight. It is not as important as C3S or C2S for the strength of cement, but it is responsible for the early strength of cement paste.Tetra calcium alumino ferrite (C4AF) is the least abundant mineral in Portland cement, accounting for about 3% of its weight. It is not as important as C3S, C2S, or C3A for the strength of cement, but it is responsible for the resistance of cement to sulfate attack.
In conclusion, the ultimate strength to cement is provided by tri-calcium silicate (C3S).