Even though there are no choices given in this particular question, the principle of osmosis is very easy to understand.
When we talk about osmosis, we are referring to the movement of water from a low concentration to a higher concentration. This is different from diffusion, which talks specifically about the movement of <em>solutes</em> in the solution (from a higher concentration to a lower concentration.)
When an RBC is placed inside a <em>hypertonic </em>solution, the water inside the RBC will go out thereby shrinking the RBC.
Inside an <em>isotonic</em> solution, the RBC will remain the same because the concentrations are equal.
Inside a <em>hypotonic</em> solution, the RBC will lyse or explode because water will move from the solution going inside the RBC.
