Final answer:
Calcium oxide is present in the largest amount in ordinary portland cement.
Step-by-step explanation:
The compound that is present in an ordinary portland cement in the largest amount is calcium oxide (CaO). Ordinary portland cement is composed mainly of four compounds: tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF).
Out of these compounds, calcium oxide (CaO) is present in the largest amount. It is formed during the process of cement production when limestone (CaCO3) is heated, resulting in the release of carbon dioxide (CO2) and the formation of calcium oxide.
Calcium oxide plays an important role in cement hydration, contributing to the strength and solidity of concrete structures.