Write the chemical formula of each of the following:
a) The compound made up of a crystal with two particles coming from chromium atoms for every three particles coming from oxygen atoms.
b) The compound made up of a crystal with one particle coming from a barium atom for every two particles coming from chlorine atoms.
c) The compound made up of molecules with 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms.
d) The compound made up of molecules with three hydrogen atoms, one phosphorus atom, and four oxygen atoms.