Critical Reasoning

Spectroscopic analysis has revealed the existence of frozen nitrogen, methane, and carbon monoxide on the surface of Pluto. Such ices have a tendency to vaporize, producing an atmosphere. Since the proportion of any gas in such an atmosphere depends directly on how readily the corresponding ice vaporizes, astronomers have concluded that the components of Pluto’s atmosphere are nitrogen, carbon monoxide, and methane, in order of decreasing abundance.

The astronomers' argument relies on which one of the following assumptions?

(A) There is no more frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane.
(B) Until space probes reach Pluto, direct analysis of the atmosphere is impossible.
(C) There is no frozen substance on the surface of Pluto that vaporizes more readily than methane but less readily than carbon monoxide.
(D) Nitrogen is found in the atmosphere of a planet only if nitrogen ice is found on the surface of that planet.
(E) A mixture of nitrogen, carbon monoxide, and methane is characteristic of the substances from which the Solar System formed.

OA is C.
I agree with the OA. However, I have a doubt with choice A. If we use the negation technique, and we assume that "there is MORE frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane". The conclusion could be weakened. Let me explain:

The argument says that the the RATE OF EVAPORIZATION of each ice (readiness) determines the proportion of each gas in the atmosphere. However, let's suppose that Nitrongen (the most abundant in atmosphere) has the lowest rate of evaporation but it is the most abundant as ice on the surface ( my negation technique). Nitrogen would be the most abundant in atmosphere not by the rate of evaporization, but by the amount of nitrogen on the surphace. The reasoning of the author would be weakened

Thanks!

Yes I totally agree with you. This is a very good point and I was also stuck between A and C.

Experts, please throw some light on this.

tough one! experts please help!

i m no expert, but here are my 2 cents:

- there is NO mention of absolute amount/volume of any gas on Pluto. The entire argument revolves around rate of vaporization and the resulting proportion of gases in the atmosphere. We cannot conclude anything about how much total volume of any gas is present on Pluto.

hope this helps!

My two cents:

Conclusion: (Amount of) Nitrogen > Carbon Monoxide > Methane.

Premise: proportion of any gas in such an atmosphere depends directly on how readily the corresponding ice vaporizes, ie. More readily some gas vaporize, more abundant it is.

Our redrwan conclusion becomes: Nitrogen vaporizes more readily than Carbon monoxide. And Carbon monoxide vaporizes more readily than methane

Lets consider A: There is no more frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane. ie Frozen Nitrogen < Frozen Carbon monoxide.

Since, Nitrogen vaporizes more readily than Carbon monoxide, amount of carbon monoxide should be less than amount of frozen nitrogen. Hence this option is not an assumption.

Can someone explain how C is correct.

Nice surprise about this shorter form. Can you tell us what it is you are talking/writing about?Has any info. about this shorter form been posted before (and i just missed it)?

Now that was an informative post to read on about the Spectroscopic analysis and how affects the existence of our atmosphere. I really appreciate the way you have explained things here in a brief and understanding manner about the Spectroscopic and thanks for the info.

metallicafan wrote:Spectroscopic analysis has revealed the existence of frozen nitrogen, methane, and carbon monoxide on the surface of Pluto. Such ices have a tendency to vaporize, producing an atmosphere. Since the proportion of any gas in such an atmosphere depends directly on how readily the corresponding ice vaporizes, astronomers have concluded that the components of Pluto’s atmosphere are nitrogen, carbon monoxide, and methane, in order of decreasing abundance.

The astronomers' argument relies on which one of the following assumptions?

(A) There is no more frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane.
(B) Until space probes reach Pluto, direct analysis of the atmosphere is impossible.
(C) There is no frozen substance on the surface of Pluto that vaporizes more readily than methane but less readily than carbon monoxide.
(D) Nitrogen is found in the atmosphere of a planet only if nitrogen ice is found on the surface of that planet.
(E) A mixture of nitrogen, carbon monoxide, and methane is characteristic of the substances from which the Solar System formed.

I received a PM requesting that I comment.

Premise:
Analysis has revealed the existence of frozen nitrogen, methane and carbon monoxide on the surface of Pluto, and such ices have a tendency to vaporize, producing an atmosphere in which the proportion of any gas depends directly on how readily the corresponding ice vaporizes.
Conclusion:
The components of Pluto's atmosphere are nitrogen, carbon monoxide, and methane, in order of decreasing abundance.

Apply the NEGATION TEST.
When the correct answer choice is negated, the conclusion will be invalidated.

C, negated:
There is A FROZEN SUBSTANCE X on the surface of Pluto that vaporizes more readily than methane but less readily than carbon monoxide.
This negation implies that the top three components of Pluto's atmosphere are nitrogen, carbon monoxide, AND X -- invalidating the conclusion that the top three components are nitrogen, carbon monoxide and METHANE.
Since the negation of C invalidates the conclusion, C is the correct assumption: WHAT MUST BE TRUE for the conclusion to be valid.

The correct answer is C.

I have a doubt with choice A. If we use the negation technique, and we assume that "there is MORE frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane". The conclusion could be weakened.

A, negated:
There is more frozen nitrogen on the surface of Pluto than there is either frozen carbon monoxide or methane.
This negation STRENGTHENS the conclusion that the top three components of Pluto's atmosphere are nitrogen, carbon monoxide and methane.
Since the negation of A does not invalidate the conclusion, eliminate A.

let's suppose that Nitrogen (the most abundant in atmosphere) has the lowest rate of evaporation

Do not make stuff up.
Nowhere in the passage or in A is it stated that nitrogen has the lowest rate of evaporation.

Phew! it's indeed a tough one.

Is it an Official CR ? What might be the difficulty level for a CR like this one on actual GMAT ?

@Verbal Experts - any thoughts ?

RBBmba@2014 wrote:Phew! it's indeed a tough one.

Is it an Official CR ? What might be the difficulty level for a CR like this one on actual GMAT ?

@Verbal Experts - any thoughts ?

The CR above appeared not on the GMAT but on the LSAT.
If this CR were to appear on the GMAT, its level would likely be 700+.