Which of the following is responsible for photochemical smog?

Given below are two statements :
Statement $I$ : If $BOD$ is $4\,ppm$ and dissolved oxygen is $8\,ppm$,then it is a good quality water.
Statement $II$ : If the concentration of zinc and nitrate salts are $5\,ppm$ each,then it can be a good quality water.
In the light of the above statements,choose the most appropriate answer from the options given below :

Which one of the following is mainly responsible for the depletion of the ozone layer?

State the harmful effects of excessive production of sulfur oxide.

$A$ man uses municipal water. Due to water scarcity,he starts using groundwater. He experiences a laxative effect. What could be the reason for this?

The pair of gases responsible for acid rain are