The molecule of \(CrO_4^{2-}\) is polar because the four oxygen atoms are arranged tetrahedrally around the central chromium atom, and the bond between chromium and each oxygen atom is polar covalent. This means that the electrons are not shared equally between the atoms, but are pulled more strongly towards the oxygen atoms, creating a partial negative charge on each oxygen atom and a partial positive charge on the chromium atom. The polarity of the bond between chromium and oxygen is due to the difference in electronegativity between the two atoms, with oxygen being more electronegative than chromium. The four polar bonds in CrO4 2- cancel each other out, resulting in a nonpolar molecule.