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22 Jan 2020, 10:40
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Oxygen-18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen. But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth. Consequently, scientists were surprised when measurements along the entire route of rain clouds’ passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant.
Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions.
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.
Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions.
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.
28 Jan 2020, 12:25
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Oxygen-18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen. But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth. Consequently, scientists were surprised when measurements along the entire route of rain clouds’ passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant.
Brilliant question. Tricky in part but easy when you get it. Question says O2 18 is rarer in cloud ⛅️ than other isotopes of O2. Lets give them some numbers 10 and 90. When it rains say 5 O2-18 isotopes fall and 3 normal isotope falls down. But the ratio 10 and 90 is maintained through the amazon. Why?
Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
This is resolve the paradox question so correct option should explain both sides of the argument.
Ans should explain why the ratio of 10 O2-18 isotope and 90 isotope is maintained? Maybe something is replenishing 5 O2 isotope and 3 other isotopes that fell during the rain. This leads us to B. Lets see other options.
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions. - does this explains both sides of the argument? No
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them. - okay, if clouds can be replenished then ratio would be same and then this will explain why scientists are surprised with their results and which they thought is contrary to their expectations. B Looks great.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.- then the isotope ratio should decrease and not stay constant.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.- uneventfully we can ignore this option. Does not resolve the paradox.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.- i hate to use out of scope but this option indeed is out of scope, doesn’t resolve the paradox, talks of indicators of rain forest
So b is our answer.
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Brilliant question. Tricky in part but easy when you get it. Question says O2 18 is rarer in cloud ⛅️ than other isotopes of O2. Lets give them some numbers 10 and 90. When it rains say 5 O2-18 isotopes fall and 3 normal isotope falls down. But the ratio 10 and 90 is maintained through the amazon. Why?
Which one of the following statements, if true, best helps to resolve the conflict between scientists’ expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds’ oxygen-18 content?
This is resolve the paradox question so correct option should explain both sides of the argument.
Ans should explain why the ratio of 10 O2-18 isotope and 90 isotope is maintained? Maybe something is replenishing 5 O2 isotope and 3 other isotopes that fell during the rain. This leads us to B. Lets see other options.
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions. - does this explains both sides of the argument? No
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them. - okay, if clouds can be replenished then ratio would be same and then this will explain why scientists are surprised with their results and which they thought is contrary to their expectations. B Looks great.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.- then the isotope ratio should decrease and not stay constant.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.- uneventfully we can ignore this option. Does not resolve the paradox.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.- i hate to use out of scope but this option indeed is out of scope, doesn’t resolve the paradox, talks of indicators of rain forest
So b is our answer.
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09 Mar 2021, 22:48
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Took me a LOOOOOONG time to actually understand the question. But once it is understood, it becomes quite easy.
For those who are struggling to understand this question, the important thing to note about the "surprise" experienced by the scientists is this:
Since a higher proportion of Oxygen-18 is showered (compared to normal Oxygen isotopes) during rain, the amount of Oxygen-18 in the clouds near the Atlantic Ocean should be more than the amount of Oxygen-18 in the clouds near the Amazon rain forests.
(Reason: a higher proportion of Oxygen-18 is showered during rain, so the amount, as well as the percentage, of O-18 should keep on decreasing as we move towards the Amazons.)
The three closest options are:
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
- Correct. This explains how O-18 content is fairly equal in all clouds.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
- Incorrect. This doesn't explain how the amount of O-18 is fairly same in all clouds.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.
- Incorrect. This doesn't explain our paradox. This option tells us:
Suppose a cloud contains 1000 units of water, and it has rained down 100 units at a location.
Out of these 100 units, (say) 20 units went to river (river runoff). THEN, exactly 20 units were recycled back to the cloud from the leaves.
But originally 100 units of rain took place... So this doesn't explain how the O-18 amount remained same.
For those who are struggling to understand this question, the important thing to note about the "surprise" experienced by the scientists is this:
Since a higher proportion of Oxygen-18 is showered (compared to normal Oxygen isotopes) during rain, the amount of Oxygen-18 in the clouds near the Atlantic Ocean should be more than the amount of Oxygen-18 in the clouds near the Amazon rain forests.
(Reason: a higher proportion of Oxygen-18 is showered during rain, so the amount, as well as the percentage, of O-18 should keep on decreasing as we move towards the Amazons.)
The three closest options are:
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
- Correct. This explains how O-18 content is fairly equal in all clouds.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
- Incorrect. This doesn't explain how the amount of O-18 is fairly same in all clouds.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of rain in river runoffs that is not recycled into the atmosphere.
- Incorrect. This doesn't explain our paradox. This option tells us:
Suppose a cloud contains 1000 units of water, and it has rained down 100 units at a location.
Out of these 100 units, (say) 20 units went to river (river runoff). THEN, exactly 20 units were recycled back to the cloud from the leaves.
But originally 100 units of rain took place... So this doesn't explain how the O-18 amount remained same.
