When a doctor needs to give someone a medication intravenously (through a vein), they dilute that medicine in a saline solution (salty water). Why would it be a bad idea for a doctor to mix the medicine with plain water? (Hint: Osmosis is the answer, but you’ll need to explain why.)

it is because the blood cells will have too much water in them and they will burst.

Explanation:

there will be less salt inside the cells so all the water will enter the cells. if there is also salt present outside of the cell then the water and the electrolites(salt) will equalize between the inside and the outside of the cell.