Halogen content and ozone

You will finish a program with three functions. The first works out the molar mass of a polyhalogen compound from its formula. The second finds the percentage of one element in it. The third finds the mass of ozone destroyed by the chlorine of a CFC.

The idea. The molar mass is the sum of the atomic masses. The percentage of an element is its mass in one mole divided by the molar mass. A chlorine atom that is regenerated destroys many ozone molecules.

Your tasks.

1. Complete molar_mass(formula), where the formula is a dictionary such as {"C": 1, "H": 1, "Cl": 3}.
2. Complete percent(element, formula).
3. Complete ozone_tonnes(kg, cl_per_molecule, chain): the tonnes of ozone destroyed by kg kilograms of a CFC of molar mass 121.0 g/mol.