Question

what key issue did the montreal protocol primarily aim to tackle?
climate change
oxygen levels
ozone layer depletion
air quality standards

Explanation:

The Montreal Protocol is an international environmental agreement. It was specifically created to address the issue of ozone layer depletion. This was mainly due to substances like chlorofluorocarbons (CFCs) which were harming the ozone layer. While climate change, oxygen levels, and air quality standards are environmental concerns, the primary focus of the Montreal Protocol is ozone layer depletion.

Answer:

ozone layer depletion