The right answer here is B. Since this is a weaken question, our job is to first zero in on the conclusion and then identify what might make that conclusion less likely. In this case, the conclusion is "the presence of these minerals in drinking water is not as detrimental as watchdog groups would have us believe." The possible trap here is that you might interpret the conclusion to be that the adsorption medium is a waste of money.

A - If anything, this might even strengthen the conclusion that these chemicals are not a problem. OUT

B - If there's a later step that removes the iron and manganese, then it is NOT the case that they are not dangerous, it is simply that some other process is removing them. This still leads to the idea that the adsorption medium is not necessary, but it refutes the conclusion that iron and manganese don't have a negative impact. CORRECT

C - This tells us nothing about the effect of iron and manganese, and adds nothing new or relevant. OUT

D - This is completely irrelevant, so what if they are? OUT

E - This is a trap answer. If most people were away, it helps to explain why there weren't any major problems. It could weaken the idea that the adsorption medium is necessary. But it in NO way suggests anything about how these metals might affect the water, and is therefore OUT

- Matoo
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Hi,
Lets break Columnist's argument.
Premise 1: Some municipal dept RECENTLY discovered a MAJOR problem with the absorptive medium.
Premise 2: THIS medium HELPS removing X & Y. BUT(trigger point) while this medium was not being used, resident suffered NO adverse health effects.
Conclusion: Presence of X & Y in drinking water is not as detrimental as groups believed.

The reason I have typed adjectives in upper case is because one should lay emphasis on them while reading. Second, trigger word showed act as an alarm because a significant information is about to be revealed which could change the course of the argument.

We are asked to weaken the columnist's argument.

How can we do this?

We could either show that X & Y are serious components (attacking the conclusion) OR present a new information, which would act like a premise, weakening the argument.



May be their absorptive media was of good quality. Loser



This is a new information saying that X & Y are removed from water by an alternative solution at a later stage. So the supplied water does not contain X & Y. This weakens/invalidates the author's argument. Contender



Still does not do anything to weaken the author's argument. Loser



Still does not do anything to weaken the author's argument. Loser



This is a trap answer choice. Fewer people to drink infected water, fewer people falling ill than the original population. But still does not weaken the author's argument. Loser

So, B is the only valid answer choice that weakens the author's argument.
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Not convinced by answer B. Both B and E seem to affect the conclusion.

Conclusion: presence of these minerals in drinking water is not as detrimental as watchdog groups would have us believe

B says wait a minute; it is not that they are not harmful, but there is another step that removes them. Similarly E says, it is not they are not harmful, rather people were away. Both seem to weaken the conclusion.

VeritasKarishma @GMATNinja@egmat@brian123

The plant's absorptive medium removes iron and manganese from water.
It was not functioning (so it was not removing these elements)
But when it was not functioning, residents suffered no ill effects.

Conclusion: presence of these minerals in drinking water is not very detrimental

We have to weaken this conclusion. A lot of things do come to mind. Perhaps the detrimental effects reflect in long term health. Or perhaps these elements were not there in the water to begin with etc.

A) No residents have fallen ill in other municipalities with similar problems with their adsorptive media.

This doesn't weaken out conclusion. If anything, it provides support to our conclusion.

B) The potassium permanganate added in a later step in the treatment process removes most of the iron and manganese from the water supply.

Correct. So these elements are removed in some other way. So the fact that the residents did not get affected doesn't mean the elements are not harmful. So the conclusion weakens.

C) Because the municipal treatment plant is so small, it was exempted from disinfection requirements after meeting certain strict criteria.

Irrelevant

D) The Commission of Environmental Quality is responsible for ensuring that the treatment processes in all municipal facilities are fully operational.

Irrelevant

E) Because it was summer, most residents of Hoopton were away on vacation when the malfunction occurred.

"Most residents" does not mean all residents. Residents did not face any adverse health effects means all residents did not face any adverse effects. Even if most of them were out, the ones here would have faced adverse effects.

Answer (B)
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Hi VeritasKarishma - wouldn’t “most” iron & manganese also not mean “all”? Since we are eliminating E on the basis of “most” not referring to “all” residents.

The passage doesn’t imply that treated water has some quantity of iron and manganese and only says “removes iron and manganese”

I am not entirely convinced if B is so much better over E to eliminate.

Posted from my mobile device

I understand your confusion but note that there is not much to be gained by deep diving into each word of non official questions. Focus on the takeaway and move on.
Normally, when the argument says "residents did not face adverse effects", I would take it to mean "people who were residing there at that time". Then "many people with homes in Hoopton were out of town at that time" would be irrelevant to us. Option (E) uses the same word though "residents of Hoopton were out" which creates a question mark.
Option (B) clearly implies that the harmful chemicals are mostly removed in some other way and that is why no harmful effects were experienced.
Official questions are usually made by putting in a lot more thought in every word and hence that kind of quality is hard to achieve.
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