Answer: The correct order is:
Potassium > calcium > chromium
Explanation:
Potassium belongs to the group of alkali metals with group number 1 in a periodic table. Potassium easily displaces hydrogen atom from the water molecule.
Where as calcium belongs to group (II) and easily displaces hydrogen atom from the water molecule.
In a reactivity series potassium is comes before the calcium metal which means that it is more reactive than calcium metal.
Potassium > calcium
Where as chromium metal is member of group 6 and chromium reacts with steam and acids to form hydroxides. But doesn't reacts with water(in liquid phase) which means it less reactive then potassium and calcium.
Potassium > calcium > chromium
