Pre-thinking:We are told the following:
In a cloudLet proportion of water molecules containing Oxygen-18 (hereafter, O-18) = x
Let proportion of water molecules containing normal Oxygen (hereafter, normal-O) = y = 1-x
y>x
During rainfall, some water molecules among x (say, a%) and some water molecules among y (say, b%) fall to the earth.
Now, a>b. So if a greater proportion of water molecules containing O-18 fall to the earth than those containing normal-O, we would expect the proportion of water molecules containing O-18 to steadily decrease over time ie; we would expect x to steadily decrease. However, measurement of clouds across the Amazon, where it rains almost daily, showed x to be constant.
Initially I thought this would be a resolve the paradox question. However, it turned out to be a much simpler inference based question!
Which one of the following inferences about an individual rain cloud is supported by the passage?
(A) Once it is formed over the Atlantic, the rain cloud contains more ordinary oxygen than oxygen-18.
This states y>x, which is true. However, I am not convinced that this is an "inference" as such, because this is quite explicitly stated in the question. At this point, we can hold on to this option. (B) Once it has passed over the Amazon, the rain cloud contains a greater-than-normal percentage of oxygen-18.
Incorrect. The passage clearly states "...the oxygen-18 content of each of the clouds remained fairly constant". Additionally, we do not know what is considered a "normal" percentage of O-18.(C) The clouds rainfall contains more oxygen-18 than ordinary oxygen.
Incorrect. We only know that a>b, which are the respective proportions of water molecules containing O-18 and normal-O. Whether the absolute quantity of O-18 in rain is greater than normal-O, we cannot say.(D) During a rainfall, the cloud must surrender the same percentage of its ordinary oxygen as of its oxygen-18.
Incorrect. The passage clearly states that a>b.(E) During a rainfall, the cloud must surrender more of its oxygen-l8 than it retains.
Incorrect. This states that a>1-a. We cannot know this for sure.Given that all other options are so obviously contradictory to the facts stated in the passage, we can select option (A).
Hope this helps.
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Crackverbal Prep Team
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