Question

they were no oxygen what changes do you observe

Answer 1

Answer:

If there were no oxygen molecules in the air, there would be fewer particles for the light to bounce off. All plants and animals require oxygen to carry out various metabolic activities. In the absence of oxygen, we would not be able to respire and life on Earth would come to an end.

Answer 2

You will see the following things:-

∆ Humans will not exist.

∆There will be no animals and plants.