Which among the following are essential constituents of Portland cement ?

Portland cement is essentially composed of calcium silicates and aluminates. Its main raw ingredients provide lime (calcium oxide, CaO), silica (SiO₂), and alumina (Al₂O₃), along with small amounts of iron oxide and gypsum. These three — silica, alumina, and lime — are the essential constituents that form tricalcium silicate, dicalcium silicate, and tricalcium aluminate upon clinkering. Neither graphite nor graphene is part of cement composition. Hence the correct answer is silica, alumina, lime.