Concentrated potassium chloride
This small plastic vial contains 10 ml of sterile water, and 10mmol of potassium chloride (KCl). That's about 0.75g of potassium chloride per ampoule. Thus, 1 litre of this will contain 1000 mmol of potassium and 1000mmol of chloride, or about 75g of potassium chloride (if one were for some reason compelled to cook it up from dry ingredients).
Thus, the osmolality of this (as it dissociates into two particles) is 2000 mOsm/Kg. Needless to say one would never give such a hyperosmolar solution via a peripheral vein.