Which of the following oxides has the lowest percentage in a usual sample of Portland cement?

The most widely used type of cement is Portland cement, which is used as a fundamental component of concrete, mortar, stucco, and non-specialty grout. It is typically created from limestone and was developed from other varieties of hydraulic lime in England at the beginning of the 19th century by Joseph Aspdin.
$\mathrm{CaO}$makes up between 50 and 60 percent of Portland cement, along with ${\mathrm{SiO}}_2$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, $\mathrm{MgO}$, 2-3%, ${\mathrm{Fe}}_2{\mathrm{O}}_3$, and ${\mathrm{SO}}_2$.
The least amount of ${\mathrm{Al}}_2{\mathrm{O}}_3$(5–10%) can be found in a typical Portland cement sample.