C) Freon initiates radical chain reactions in the stratosphere.

In the stratosphere, the ozone layer plays a crucial role in protecting life on Earth by absorbing most of the sun's harmful ultraviolet (UV) radiation. However, certain substances can disrupt the ozone layer, leading to ozone depletion. One such group of substances is chlorofluorocarbons (CFCs), commonly known by the trade name "Freon."

Freon is composed of carbon, chlorine, and fluorine atoms, and it is widely used as a refrigerant, propellant, and solvent. When released into the atmosphere, Freon molecules can rise to the stratosphere due to their stability and low reactivity in the lower atmosphere.

Once in the stratosphere, Freon molecules can be broken down by solar UV radiation, specifically UV-C and UV-B rays. This process, known as photodissociation, breaks the carbon-chlorine bond in Freon molecules, resulting in the release of chlorine radicals (Cl●). These chlorine radicals are highly reactive and can initiate radical chain reactions.

The chlorine radicals can then react with ozone (O₃) molecules, leading to the destruction of ozone. The reaction between chlorine radicals and ozone is a catalytic cycle, meaning that a single chlorine radical can destroy multiple ozone molecules before being eventually deactivated.

The overall reaction can be summarized as follows:
Cl● + O₃ → ClO● + O₂
ClO● + O → Cl● + O₂
The net effect is the depletion of ozone molecules in the stratosphere.

Ozone depletion is a serious environmental concern as it allows more UV radiation to reach the Earth's surface, increasing the risk of skin cancer, cataracts, and other harmful effects on both human and animal health.

It is important to note that not all substances can initiate radical chain reactions in the stratosphere. Iodoform, as mentioned in option b, is not a significant contributor to ozone depletion. Chloroform, as mentioned in option d, is also not a major concern for ozone depletion compared to Freon.

In conclusion, option c is the correct answer as Freon, or chlorofluorocarbons, can indeed initiate radical chain reactions in the stratosphere, leading to the depletion of the ozone layer.