Question

Assertion (A): Osmotic pressure is the function of solute concentration.
Reason (R): The more solute concentration the greater will be the pressure required to prevent water from diffusing in

• A. Both (A) and (R) are correct and (R) is the correct explanation to (A)
• B. Both (A) and (R) are correct but (R) is not correct explanation for (A)
• C. (A) is correct (R) is wrong
• D. (A) is wrong (R) is correct

Hint:

Osmotic pressure (\(\pi\)) is numerically equivalent to osmotic potential (\(\Psi_{s}\)), but with a positive sign.
More solute \(\rightarrow\) lower \(\Psi_{s}\) (negative value) \(\rightarrow\) higher osmotic pressure (\(\pi\), positive value).

Answer 1

The Correct Option is A

Step 1: Write down the governing relation.
Osmotic pressure follows $\pi = iCRT$, where $C$ is the solute concentration and $i$, $R$, $T$ are constants for a given solute and temperature, so $\pi$ rises in direct proportion to $C$. This confirms the Assertion.
Step 2: Translate the formula into plain words.
A solution with more dissolved solute pulls water in more strongly across a semipermeable membrane, so you need to push back with more external pressure to stop that inward pull, which is precisely what the Reason states.
Step 3: Connect formula to statement.
Since the formula shows pressure scaling directly with concentration, the everyday description in the Reason, more solute needing more counter pressure, is just the formula written in words, so it explains the Assertion perfectly.
Final answer: Option 1, both statements are correct and the Reason correctly explains the Assertion.