Fluoride enters a region's groundwater when rain dissolves fluoride

Question

Fluoride enters a region's groundwater when rain dissolves fluoride-bearing minerals in the soil. In a recent study, researchers found that when rainfall, concentrations of fluoride-bearing minerals, and other relevant variables are held constant, fluoride concentrations in groundwater are significantly higher in areas where the groundwater also contains a high concentration of sodium.

Which one of the following can most reasonably be concluded on the basis of the researchers' findings?

(A) Fluoride-bearing minerals are not the primary source of fluoride found in groundwater.
(B) Rainfall does not affect fluoride concentrations in groundwater.
(C) Sodium-bearing minerals dissolve at a faster rate than fluoride-bearing minerals.
(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve.
(E) Soil that contains high concentrations of sodium-bearing minerals also contains high concentrations of fluoride-bearing minerals.

Source: LSAT

SonalSinha803 · Answer

(A) Fluoride-bearing minerals are not the primary source of fluoride found in groundwater. -
No information on primary source. Irrelevant

(B) Rainfall does not affect fluoride concentrations in groundwater. - It does as stated in the argument. Incorrect.

(C) Sodium-bearing minerals dissolve at a faster rate than fluoride-bearing minerals.
- It is not about comparison b/w sodium bearing and fluoride bearing minerals. Irrelevant

(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve.
- this concludes well taking into consideration the premise. Correct

(E) Soil that contains high concentrations of sodium-bearing minerals also contains high concentrations of fluoride-bearing minerals. - We are not talking about soil. Neither does it conclude well from the premise.

IMO D.

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push12345 · Answer

We need to take into account things which Are already mentioned in passage.no new element is required

A) Fluoride-bearing minerals are not the primary source of fluoride found in groundwater.
  primary source-new element so out

(B) Rainfall does not affect fluoride concentrations in groundwater.  its too strong.we are not sure about this as we have info only when rainfall held constant

(C) Sodium-bearing minerals dissolve at a faster rate than fluoride-bearing minerals. not sure as we know where flouride is max sodium also max but whether sodium dissolve more nor not.cant say

(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve. where flouride max ,so sodium max. So there can be reason that sodium help in some way to max flouride.lets keep it

(E) Soil that contains high concentrations of sodium-bearing minerals also contains high concentrations of fluoride-bearing minerals. last sentence says where flouride max, sodium max but vice versa we can't say so out

So best choice we have is D

Give kudos if it helps

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VodkaHelps · Answer

Hi Experts!

I can't understand this argument as it says in the premise that in the research "concentrations of fluoride-bearing minerals, and other relevant variables are held constant," - means rainfail did not actually dissolve the flouride-bearing minerals yet if the groundwater contains a high concentration of sodium, the flouride concentration is significantly higher.

I cannot come up with the logic of answer D which states that the sodium level increases at the rate of flouride dissolving. How could we conclude that?

Thank you

redskull1 · Answer

Can someone please tell how D is correct in the context of E being incorrect

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IshanVirdhi · Answer

premise states
a) given rainfall,  concentration of F minerals  and other relevant variables kept constant (in other words equal in both the scenario) except for Sodium. Sodium concentration increases - > Flourite concentration in groundwater increases.

Lets review D and E

D) This option choice can be REASONABLY concluded as all other factors are constant.
E) Since we are told that concentration of fluorite was kept constant, this option choice directly contradicts the premise

Hardik0007 · Answer

fluoride concentrations in groundwater are significantly higher in areas where the groundwater also contains a high concentration of sodium.

The above line clearly states the relation between Floride and sodium concentration in soil.Therefore Answer is pretty straightforward "D".

(A) Fluoride-bearing minerals are not the primary source of fluoride found in groundwater.  No, it's Illogical 
(B) Rainfall does not affect fluoride concentrations in groundwater. rain dissolves fluoride-bearing minerals in the soil, so irrelevant  
(C) Sodium-bearing minerals dissolve at a faster rate than fluoride-bearing minerals.  out of scope 
(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve. yes, this is the what statement concludes. 
(E) Soil that contains high concentrations of sodium-bearing minerals also contains high concentrations of fluoride-bearing minerals again, irrelevant

analytica233 · Answer

(B) Rainfall DOES NOT AFFECT fluoride concentrations IN GROUNDWATER
This can not be drawn from argument because the argument states that "Fluoride enters a region's groundwater WHEN RAIN DISSOLVES fluoride-bearing minerals in the soil."

(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve.
The argument says that if rainfall, concentrations of fluoride-bearing minerals, and OTHER relevant variables are HELD CONSTANT, fluoride concentrations are SIGNIFICANTLY HIGHER in areas where the groundwater ALSO CONTAINS a high concentration of sodium. Hence, concentration of sodium in groundwater AFFECTS concentration of fluoride in groundwater. (D) says "the RATE at which fluoride-bearing minerals DISSOLVE" because concentrations of fluoride-bearing minerals are held constant: concentrations of fluoride IN MINERALS are the same, but sodium increases the RATE at which fluoride-bearing minerals dissolve in the GROUNDWATER. (D) is correct.

shameekv1989 · Answer

analytica233  :- Wouldn't the concentration depend on the time the readings are taken?

What I mean is if it is taken during the time when rain is falling then it would make sense that keeping the fluoride minerals same in an area Fluoride concentrations would change with the rate at which sodium dissolves the fluoride minerals. Because then we will have different readings at different times with the rates.

But if the readings are taken after the complete rainfall or at a time when all the fluoride minerals are dissolved in an area. We would have the Fluoride concentration accounted by Flouride minerals as same which would mean that we can not conclude about the rate at which sodium dissolves these minerals.

Or I have just misunderstood the argument all together.

unraveled · Answer

Fluoride enters a region's groundwater when rain dissolves fluoride-bearing minerals in the soil. In a recent study, researchers found that when rainfall, concentrations of fluoride-bearing minerals, and other relevant variables are  held constant ,  fluoride concentrations in groundwater are significantly higher  in areas where the  groundwater also contains a high concentration of sodium .

Which one of the following can most reasonably be concluded on the basis of the researchers' findings?

(A) Fluoride-bearing minerals  are not the primary source  of fluoride found in groundwater.
(B) Rainfall  does not affect  fluoride concentrations in groundwater.
(C) Sodium-bearing minerals  dissolve at a faster rate than  fluoride-bearing minerals.
(D) Sodium in groundwater increases the rate at which fluoride-bearing minerals dissolve.
(E) Soil that contains high concentrations of sodium-bearing minerals  also  contains  high concentrations  of fluoride-bearing minerals.

If one understood the passage clearly, then sodium does something that other factors don't. So, we need to find a choice that elaborates what and how sodium does/does so.
Also, we need to question each choice for what it says and why. Doing so helps us to know that only C and D are the rightful contenders. 
C is comparing the rate of dissolution which in the passage is nowhere found.

At best, if one sees the passage content as paradox then only D helps resolve the puzzle though a small one.

Answer D.

Suyash1331 · Answer

E also shows a relation between floride and sodium concentration in soil. then why E is irrelevant

Fluoride enters a region's groundwater when rain dissolves fluoride

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Fluoride enters a region's groundwater when rain dissolves fluoride

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