Spectroscopic analysis has revealed the existence of frozen nitrogen, methane, and carbon monoxide on the surface of ...

Sangwook on June 18, 2014

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I chose (c) by eliminating the others. So, could you please explain why (c) is the correct assumption? Thanks

2 Replies

Melody on June 25, 2014

Here we have a Strengthen with Necessary Premise question. Remember that a premise is necessary for a conclusion if the falsity of the premise guarantees or brings about the falsity of the conclusion. First, we check to see if the answer choice strengthens the passage, and then, if it does strengthen, we negate the answer choice to see if its negation makes the argument fall apart. If the answer choice does both those things then it is our correct answer.

The conclusion of this argument is, "the components of Pluto's atmosphere are nitrogen, carbon monoxide, and methane, in order of decreasing abundance." Why? Evidence has shown that frozen nitrogen, methane, and carbon monoxide exist on the surface of Pluto. We know that these ices have a tendency to vaporize, producing an atmosphere. We are also told that the proportion of a gas in an atmosphere relies on how readily the corresponding ice vaporizes.

We only know that frozen nitrogen, methane and carbon monoxide exist on the surface of Pluto. We do not know if those are the only components found on the surface. We also don't know in what proportion they are found. However, merely from their existence, and the fact that the proportion of gas in the atmosphere depends on how readily the ice vaporizes, we come to our conclusion. What if there are other frozen gases trapped in the ice? We are lacking some essential information here.

That is why answer choice (C) is our answer. First, it strengthens the argument because it succinctly tells us that there are no other frozen substances that vaporize more readily than methane, but less readily than carbon monoxide, meaning that our conclusion that Pluto's atmosphere is made up of nitrogen, carbon monoxide and methane, in order of decreasing abundance is supported.

Next, we have to see if the negated version of the answer makes our argument fall apart. The negation of (C) is: "There is some frozen substance on the surface of Pluto that vaporizes more readily than methane, but less readily than carbon monoxide." If this is the case, the conclusion is no longer correct because the components of Pluto's atmosphere are not complete, i.e. we should include the frozen substance that vaporizes more readily than methane but less readily than carbon monoxide in our conclusion.

Therefore, answer choice (C) is our answer because our two-tiered check system for the correct answer has been completed.

Hope that helps! Let us know if you have any other questions.

Sangwook on July 2, 2014

Thanks a lot!!!^^