Which chemical is considered the least damaging to the stratospheric ozone layer?

The correct choice is HCFCs. Hydrochlorofluorocarbons (HCFCs) are regarded as being less damaging to the stratospheric ozone layer compared to other options like CFCs (chlorofluorocarbons), methyl bromide, and halon.

HCFCs are designed with a lower ozone depletion potential than CFCs, which are known to significantly contribute to ozone layer depletion due to their stability and ability to release chlorine atoms in the stratosphere. While they still have some ozone-depleting potential—hence their phased reduction under international agreements like the Montreal Protocol—they are much less harmful than CFCs.

Methyl bromide and halon also have substantial impacts on the ozone layer. Methyl bromide is a widely used pesticide that can lead to ozone depletion, and halons are substances used in fire extinguishers, known for their high ozone-depleting qualities due to the release of bromine atoms.

In summary, HCFCs are a transitional alternative that poses relatively lower risks to the ozone layer, making them the choice that represents a step towards reducing ozone depletion, even though their use is also being phased out in favor of even safer alternatives.