Critical Reasoning

The popular view is that Ozone layer's depletion is real, as certain as Neil Armstrong's landing on the moon. While that may be the case, the attribution of such depletion to man-made chemicals is not true. Mount Pinatubo in the Philippines spewed forth more than a thousand times the amount of ozone-depleting chemicals in one volcanic eruption than all the fluorocarbons manufactured by wicked, diabolical and insensitive corporations in history. Mankind can't possibly equal the output of even one eruption from Pinatubo, much less 4 billion years' worth of them, so how can it be held responsible for destroying ozone.

Which of the following is an assumption on which the argument of the author depends?

A) It would take mankind more than 4 billion years to destroy Ozone.
B) Each molecule of ozone depleting chemical released during an eruption of Mount Pinatubo destroys the same quantity of ozone as a molecule of fluorocarbons.
C) The amount of ozone-depleting chemicals released during a single eruption in Mount Pinatubo is much higher than the quantity of fluorocarbons produced by the companies
D) The molecular structure of ozone-depleting chemicals released during a volcanic eruption does not prevent them from reaching the stratosphere, the layer of the atmosphere where the ozone layer resides.
E) The rate at which an ozone depleting chemical, whether man-made or released in a volcanic eruption, is released is not more important in the destruction of ozone layer than the quantity of chemicals released.

Please provide detailed explanations.

B seems to be a very good option.

We have not been told anything about the nature of the Ozone Depleting Chemicals (ODC for short). So we don't know anything about the mechanism in which they react with the ozone. What if one molecule of the man-made CDCs molecules destroy a million while one molecule of Volcanic CDCs destroy just one molecule of ozone (actually we know this is possible since ozone depletion takes place through free radical mechanism and once molecule of CDC can destroy many molecules of ozone). In that case there is no basis for comparison between man made CDC and artificial CDC.

Since negation of B yields the possibility discussed above, B ought to be a good option.

TheGraduate wrote:B seems to be a very good option.

We have not been told anything about the nature of the Ozone Depleting Chemicals (ODC for short). So we don't know anything about the mechanism in which they react with the ozone. What if one molecule of the man-made CDCs molecules destroy a million while one molecule of Volcanic CDCs destroy just one molecule of ozone (actually we know this is possible since ozone depletion takes place through free radical mechanism and once molecule of CDC can destroy many molecules of ozone). In that case there is no basis for comparison between man made CDC and artificial CDC.

Since negation of B yields the possibility discussed above, B ought to be a good option.

B does seem to be a good option, but the truth is that there is something about B that can be used to eliminate it.

B says that each molecule of chemical from the volcano is equally as destructive to the ozone layer as each fluorocarbon molecule.

The prompt says that the volcano spewed " ... more than a thousand times the amount of ozone-depleting chemicals in one volcanic eruption than all the fluorocarbons ..."

Does B have to be true?

First of all, we don't even know what "more than a thousand times" means. Does that mean "more than a thousand times the molecules"?

Let's say that it does, and that B is not true.

What if the molecules from the eruption are only 1/100 as ozone destroying as fluorocarbon molecules? 1000/100 is still 10. So in one eruption the volcano could still have ten times the effect of all fluorocarbons ever produced.

Alternatively, the molecules from the volcano could be, rather than equally destructive, much more destructive.

So, B is a classic trap answer, one that sounds great, RIGHT!, while what it says does not have to be true in order for the argument to work.

On the other hand, were D not true, then the argument would be destroyed, because in that case the chemicals from the volcano would not reach the ozone layer.

The correct answer is D.

Premise: The volcano destroyed ozone far greater than humans till now.

Conclusion: Humans shouldn't be held responsible for the destruction of ozone.

B doesn't really impacts the conclusion..

All we have to do is to show that mankind isn't responsible as much as the volcano is in the destruction of ozone.