A simple of helium has a volume of 521 dm3 at a pressure of 75 cm Hg and a temperature of 18°C. When the temperature is increased to 23° C, what is the volume of the helium?

It will fall off and tip over. 

Conservation efforts have been effective in "increasing the number of endangered species, reducing all the negative impacts of human activity, and preserving wildlife habitats".hope my answer has you : ) 

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.