Question 84·200 Super-Hard SAT Reading Questions·Expression of Ideas
While researching the chemical analysis of historical textiles, a student has taken the following notes:
- Researchers examined a purple thread from a seventeenth-century tapestry.
- Raman spectroscopy revealed vibrational bands characteristic of an indigo molecular framework.
- Fluorescence from the thread obscured weaker Raman bands that could have shown whether bromine atoms were attached to that framework.
- X-ray fluorescence spectroscopy (XRF) detected bromine in the thread.
- XRF can identify the elements in a sample but cannot show how those elements are arranged within molecules.
- Reference analyses indicate that 6,6′-dibromoindigo, the principal colorant in shellfish purple, contains both an indigo framework and attached bromine atoms.
The student wants to explain why combining Raman spectroscopy and XRF, rather than relying on either technique alone, supported the researchers’ identification of the thread’s colorant. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions, translate the student’s goal into a checklist before comparing the choices. Here, the response must include the relevant finding and limitation of each technique and explain how the findings complement each other. Reject choices that merely list results, overstate what one method proves, or confuse the methods’ capabilities.
Hints
Focus on the stated goal
Look for a choice that explains both why the techniques were combined and why neither technique was sufficient by itself.
Separate the capabilities
Determine which technique supplied information about molecular structure and which supplied information about elemental composition.
Avoid overstatements
Eliminate any choice claiming that one technique independently identified the exact compound or revealed information that the notes say it cannot provide.
Step-by-step Explanation
Identify the required relationship
The goal is not merely to summarize the findings. The response must explain why the identification depended on combining the two techniques rather than using either one alone.
Evaluate the Raman evidence
Raman spectroscopy revealed an indigo framework, but fluorescence prevented it from showing whether bromine atoms were attached. Thus, Raman provided useful but incomplete molecular evidence.
Combine the XRF evidence
XRF detected bromine but could not determine the molecular framework containing it. Since reference analyses associate both an indigo framework and attached bromine with 6,6′-dibromoindigo, the two incomplete but complementary findings jointly support the identification.