What is the difference between a mixture, compound, element and pure substance

Why are the trends and exceptions to the trends in ionization energy observed?

What is the temperature of one mole of helium gas at stp?

According to the kinetic-molecular theory, what happens to a liquid when it is transferred from one container to another? the volume and the shape stay the same. the volume increases to fill the new container, but the shape stays the same. the volume stays the same, but the shape changes to fit the new container. the volume and the shape change to fill the new container.