Step 1: Understanding the Concept:
Evaluate various colligative properties (Osmotic pressure, elevation of boiling point, relative lowering of vapor pressure) and concentration units. Colligative properties rely strictly on the total number of solute particles (ions/molecules) in the solution, governed by the Van't Hoff factor ($i$).
Step 2: Key Formula or Approach:
For colligative properties, apply the formulas: $\pi = iCRT$ and $\Delta T_{b} = iK_{b}m$. Compare $i$ values: $NaCl$ ($i \approx 2$) vs. Urea ($i = 1$). Compare concentration magnitudes for $ppm$ vs. Molarity.
Step 3: Detailed Explanation:
(A) Osmotic Pressure ($\pi$): For the same molarity ($C$), $\pi$ depends on $i$. $NaCl$ dissociates into 2 ions ($i=2$), while Urea is a non-electrolyte ($i=1$). Thus, $\pi_{NaCl}>\pi_{Urea}$. The given statement is reversed. (Incorrect)
(B) Concentration: Parts per million ($ppm$) is for highly dilute traces. $2$ M of $NaCl$ is roughly $117$ g per Liter ($117,000$ mg/L or ppm). Clearly, $2$ ppm is exponentially smaller than $2$ M. (Incorrect)
(C) Elevation in Boiling Point ($\Delta T_{b}$): Similar to osmotic pressure, for equal concentrations, $NaCl$ ($i=2$) creates a higher elevation in boiling point than Urea ($i=1$). Thus, $\Delta T_{b \text{ (NaCl)}}>\Delta T_{b \text{ (Urea)}}$. (Incorrect)
(D) Vapour Pressure: Raoult's Law states that the addition of a non-volatile solute (like salt) to a pure solvent (water) physically blocks solvent molecules from escaping, which continuously lowers the vapour pressure. Thus, salt water has a strictly lower Vapour Pressure than pure water. (Correct)
Step 4: Final Answer:
Option (D) is the correct statement.