Here's why:

* Cr represents the element Chromium.

* O represents the element Oxygen.

* The subscript 2 after Cr indicates there are two Chromium atoms in the compound.

* The subscript 3 after O indicates there are three Oxygen atoms in the compound.

* The Roman numeral III in Chromium(III) oxide indicates the oxidation state of Chromium, which is +3 in this compound.

This formula is commonly used to describe a green powder that has various applications in pigments, ceramics, and polishing.