Sea water is modelled as $0.50\mathrm{M}$ $\mathrm{NaCl}$ (complete dissociation) at $300\mathrm{K}$, with $R=0.0821\mathrm{L}\mathrm{atm}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-1}$. It is subjected to reverse osmosis. Which statements are correct?

1. AApplying 30 atm on the sea-water side will initially drive pure water through the membrane.
2. BThe osmotic pressure of the sea water is about 24.6 atm.
3. CAs water is removed, the remaining brine becomes more concentrated, so the pressure needed rises.
4. DApplying 20 atm on the sea-water side will initially drive pure water through the membrane.