World Geography
The relative abundance of dissolved salts in seawater in descending order is as follows

chlorine, sodium, sulphate, magnesium, calcium, potassium
sodium, chlorine, magnesium, potassium, sulphate, calcium
chlorine, magnesium, calcium, sodium, potassium, sulphate
chlorine, sodium, magnesium, calcium, potassium, sulphate

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World Geography
The main objective of multi-purpose river projects are

power generation by constructing hydro power stations
extension of irrigation facilities by constructing dams to store surplus water during the rainy seas
flood controls and making rivers navigable
All of these

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