is it true that all elements are made up of at least one of these elements air, fire, water and earth

What does the process of natural selection involve

Which of the following is true for the actual yield of a reaction? it is always calculated as a ratio. it is the yield from the excess reactant. it is the yield from the limiting reactant. it is always less than the theoretical yield.

What shape would a molecule with two bound groups and two lone pairs have?