In an ionic formula, the positions of number ions are represented by their respective subscripts. Subscripts are small numbers written after the chemical symbol of an element to indicate the number of atoms of that element in a compound.

For example, in the ionic formula NaCl, the subscript "1" after the "Na" symbol indicates that there is one sodium ion in the compound, while the subscript "1" after the "Cl" symbol indicates that there is one chloride ion in the compound.

Similarly, in the ionic formula Fe2O3, the subscript "2" after the "Fe" symbol indicates that there are two iron ions in the compound, while the subscript "3" after the "O" symbol indicates that there are three oxygen ions in the compound.

Therefore, the position of number ions in an ionic formula is indicated by their respective subscripts.