Suppose a student heat a sample of the metal in air to form its oxide and use the mass data to obtain a volume of 21.949 for the equivalent weight. What is the equivalent weight of calcium?

In any atom of any element, you will find protons and neutrons in the nucleus of any atom 

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.