#26 - Concept Reference, Must Be True

[Adam Tyson]

Stick with the info from the passage, RajPatel, and not any outside info. Here, the author told us that the lower atmosphere is the troposphere, and that CFCs released there drift upwards into the stratosphere, where they have those problematic reactions. If we were looking for a replacement for CFCs, what good would it do us to look at how it behaves in the lower atmosphere? And what is this bit about chemicals "commonly found" there? Do CFCs have something to do with chemicals commonly found somewhere? Don't we want to know whether those chemicals would drift upwards, like CFC does, and what they would do up in the stratosphere? Would they release chlorine, or something like chlorine, that would damage the ozone layer? Also, is "reacting" by itself a problem, or is it only certain types of reactions that matter?

Your goal in this question is to select an answer that asks a crucial question, one that will help us better analyze a potential replacement for CFCs. This is a lot like an Evaluate the Argument question in LR, where you have to find the answer that asks the right question.

Try a thought experiment here: imagine that we are testing a potential replacement for CFCs. Let's say we are testing XYZs to see if they will do the job. Now imagine that we conduct a test to see whether XYZs react with chemicals commonly found in the lower atmosphere. What are the possible outcomes? It's either "yes, they do react" or "no, they do not react." What impact would a Yes have on our analysis? Would that mean they are not an acceptable replacement? What if the answer is No, they do not react - would that mean they are okay as a replacement? I think in either case we would be left unsure, because we wouldn't know what might happen to the ozone as a result of any of that. Are those reactions good for it, bad for it, or neutral? Would XYZs even interact with the ozone?

Since answer B doesn't ask a particularly crucial question, and answer D asks one that is more salient, answer B is not the most useful question to ask. It's not wrong to ask it, but it's just not as important to ask as answer D is. If XYZs contain parts that are similar to chlorine, the main culprit in the destruction of the ozone, that would be very useful to know. It wouldn't tell us for sure whether they are an acceptable replacement or not, but at least we would have some valuable information that would help in making that determination.

Answer B isn't a wrong answer - it's just not the best answer, and we always want the one that is best. Don't just look at answer B in isolation, but compare it to answer D. What makes one of them more useful than the other? Don't just go for an answer that could work, or that might be okay. Go for the one that is better than the other four choices!

[fork4k]

Both D and E seemed like the least wrong answers of the bunch to me, but both seemed to underdetermine the prompt.

D wasn't really adequate since even if the chemical shared nothing in common with chlorine it could've shared things in common with some other element that was also damaging to the atmosphere (and nowhere in the passage does it say chlorine is the only constituent of CFC that's bad for the ozone layer).

E also felt inadequate since even if it didn't break down into its components it could still be bad for the atmosphere. I ended up going with E, arbitrarily.

In a situation like this where both answers seem to be not fully correct, how do you decide between them? It isn't clear to me why D is any "more" correct than E.

[Adam Tyson]

The question asks which of these would be most useful to know, fork4k. That doesn't mean that the correct answer will completely settle the question of whether a particular chemical would be an acceptable replacement. it's just the one issue, from among the five answer choices, that would be most important to know.

Answer E does nothing. So what if the replacement breaks down? That doesn't tell us anything about whether it's a good replacement or not. What if it does not break down? Is that a good thing, or a bad thing? This information is not useful without something more.

But knowing whether it has something in common with chlorine would be very important, because chlorine was the big problem for the ozone. While that doesn't completely settle the issue, it's the kind of thing we should care about, a lot. What if it's exactly like chlorine? That would be bad! What if it's nothing like chlorine? That at least gives us some hope that it won't be a problem. Does it prove it? No. But it's still something useful to know, one way or the other, and that makes it the best answer of the ones presented.

[dshin117]

I have two problems with AC (D), many of which have been echoed by fellow students.

For starters, nowhere in the passage is it stated that chlorine is the most or the ONLY damaging substance to the ozone. I can grant "the most" because that's clearly what's supported per question 23 (another question I got wrong). But the only? Even if we grant that it's the most, how do we know there isn't another chemical that is also really bad for the ozone? Eliminating chlorine from contention doesn't necessarily mean it won't be damaging to the ozone layer. Also, and this is my second point of contention, who even says we are eliminating chlorine from contention? So what if its chemical properties are alike with chlorine? There are many chemicals whose properties are similar, yet react completely differently to a given environment. By contrast, there are many chemicals whose properties are similar yet react the same in a given environment. The key is the harmful REACTION with ozone and simply saying a chemical has similar properties doesn't indicate that it will or won't react a certain way.

By contrast, in AC (D), if we cut out the possibility of a reaction altogether, wouldn't that better guarantee that there would be no damage to the ozone layer altogether? We're cutting the very possibility of damage altogether if there is no breakdown because the passage says the UV light "breaks them down" into their constituent, harmful elements.

Let's say we are asked whether the chemical in question breaks down into its components when subject to UV radiation. If the answer is yes, then we don't know how damaging it would be because it could contain chlorine. By contrast however, if the answer is no, then we know it won't be damaging because it doesn't matter whatever harmful constituent element it contains (I don't buy the whole 'what if we shot chlorine up in the sky' argument because chlorine's a constituent ELEMENT of a chemical not the chemical itself and we are asked to determine whether a CHEMICAL would be harmful).

[Amber Thomas]

Hi dshin117!

Let's reference the section in the passage that discusses chlorine (Lines 24-33):

"There, subjected to massive ultraviolet radiation, [the freon gases] break down into their constituent elements, including chlorine. The resulting increase in the concentration of chlorine in the stratosphere is devastating to the ozone layer. Chlorine and ozone chemically react in a way that both destroys the ozone and regenerates the chlorine atoms. As a result of this chemical reaction, each chlorine atom could destroy as many as 100,000 ozone molecules before becoming inactive."

So, we know that chlorine is extremely harmful to the ozone layer, it is perhaps even the most harmful chemical to the ozone layer. Therefore, it would logically follow that chemicals with similar properties to chlorine would have a similarly negative effect on the ozone layer. So, we would want to rule out any chemicals/components that could react in a similar way to chlorine, and would therefore harm the ozone layer.

As Athena mentioned earlier in this thread, the UV light breaking down these chemicals in the atmosphere isn't the problem-- the chlorine is the problem. If the UV light broke down harmless chemicals into harmless constituent parts, that wouldn't negatively impact the ozone layer. Really, what we want to do is to make sure that chlorine, and similarly-reacting harmful chemicals stay away from the ozone layer.

I hope this helps!