Urgent answerwhy is it important that a pure water iv not be given to dehydrated patients?

Pure water is never given IV. It could be disastrous. It would be hypotonic. Red blood cells lysis would occur due to the osmotic gradient. A large volume of pure water IV would play havoc with blood osmolarity. That's why 5% dextrose is given if one does not wish to give saline solutions. 
MD answer

The answer is option b.