Q1: Pick up the compound responsible for early strength of cement from the following:

ANS:B - Tricalcium silicate

Initial setting is responsible by aluminate as it first compounds to react but early strength is provided by tricalcium silicate and ultimate strength is by dicalcium silicate. C3S - Early strength, rapid hardening, more heat.
C3A - Initial setting time, Quickest to react with water. Tricalcium Silicate (C3S) hardens rapidly and is largely responsible for initial set and early strength. In general, the early strength of Portland cement concrete is higher with increased percentages of C3S. Dicalcium Silicate (C2S) hardens slowly and contributes largely to strength increases at ages beyond 7 days. C3S - Early strength.
C2S - Strength lateral.
C3A - Setting time.