Step 1: Meet osmotic pressure.
Osmotic pressure $\pi$ is the pressure needed to stop water from flowing into a solution through a semi permeable wall. We must find its correct formula.
Step 2: Start from the gas law idea.
The behaviour of a dilute solution is like a gas. The ideal gas law is $PV = nRT$. We bend this idea to fit a solution.
Step 3: Bring in concentration.
Rewrite the gas law as $P = \frac{n}{V} RT$. The ratio $\frac{n}{V}$ is the concentration $C$, in moles per litre.
Step 4: Replace with C.
Putting $C = \frac{n}{V}$ gives\[ \pi = CRT \]
Step 5: Check the units make sense.
Here $C$ is concentration, $R$ is the gas constant and $T$ is the absolute temperature. Together they give a pressure, which is what we want.
Step 6: Final choice.
So the correct relation is $\pi = CRT$.\[ \boxed{\pi = CRT} \]