Use Slater's rules to estimate Zeff for the 4f and valence electrons of Hg2+ and O2−; assume for this purpose that all the inner electrons with (n - 3) or less screen a full +1. Express your answers using two decimal places separated by commas.

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck

The velocity would be 2 

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.