Equal masses ($1.0\mathrm{g}{\mathrm{L}}^{-1}$) of the following are dissolved separately in water: urea (M = 60), $\mathrm{NaCl}$ (M = 58.5, assume complete dissociation), a macromolecular colloid (M = $1.0\times 10^5$) and a gold sol whose particles each contain $1.0\times 10^6$ Au atoms (Au = 197). Taking ideal behaviour, the decreasing order of osmotic pressure is

1. Aurea $>$ $\mathrm{NaCl}$ $>$ macromolecule $>$ gold sol
2. B$\mathrm{NaCl}$ $>$ urea $>$ macromolecule $>$ gold sol
3. C$\mathrm{NaCl}$ $>$ urea $>$ gold sol $>$ macromolecule
4. Dmacromolecule $>$ $\mathrm{NaCl}$ $>$ urea $>$ gold sol