When naming a transition metal ion that can have more than a common ion charge the numerical value of the charge is indicated by a . superscript after the name.
b. suffix.
c. prefix.
d. roman numeral following the name.

When naming a transition metal ion that can have more than a common ion charge the numerical value of the charge is indicated by a Roman numeral following the name (option d)

Explanation:

In these cases the stock system is used: this type of nomenclature names the compounds ending with the valence indicated in Roman numerals. That is, Roman numerals are placed to indicate the oxidation states of the elements. These numbers are placed at the end of the name of the transition metal ion.

Examples of this are: Iron (III) or Chromium (II)

The independent variable would be salt water since it never changes since they all get the same amount.

The dependent variable would be the height of the plant because all of them might grow differently depending on the amount of salt in the water given.

The constant variable would be sunlight because it always get the same amount everyday.