hard · GMAT Verbal
In reverse-osmosis desalination, energy is spent pushing seawater against osmotic pressure to force pure water through a membrane. Thermodynamics sets a minimum energy per liter that no membrane can reduce, because it is fixed by the salt concentration itself. Real plants already operate close to that minimum. Newer membranes mainly let water pass with less resistance, raising throughput.
The statements above, if true, most strongly support which of the following?
- Reverse osmosis will eventually become cheaper than every alternative method of producing fresh water.
- Improving membranes alone cannot bring the energy needed per liter of desalinated water below the thermodynamic minimum.
- The energy required to desalinate seawater could be eliminated by a sufficiently advanced membrane.
- Desalinating water with a lower salt concentration would require more energy per liter than desalinating seawater.
- Future membrane improvements will have no effect whatever on the operating costs of desalination plants.
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