The Correct Answer is (D) — Whenever a question contains the phrase “of the following,” you should look at the answer choices before making a prediction. The mass of the metals was always 100g, so that was precisely controlled, and you can eliminate (A). The metals were each exposed to the flame for 30 seconds, so that was precisely controlled as well, and you can eliminate (B). The only measurements related to the height of the clamp and the temperature of the flame are “at a fixed height” and “medium intensity,” respectively. Neither of these is very specific, but you have to decide which one was more precisely controlled. Even though you don’t know anything about the height of the clamp, you know it remained the same; therefore, it was precisely controlled, just not measured or recorded, and you can eliminate (C). There was no precise attempt to keep the temperature of the flame constant, however. “Medium intensity” could refer to a very wide range of temperatures, and the temperature of a medium intensity flame could have fluctuated throughout each experiment.


The Correct Answer is (H) — This question asks you which procedure would help you determine what type of metal U4 is, given that it produced a gray-white color after 20 seconds of being burned, and turned no other color. (J) is incorrect because the data for unknown metal U4 doesn’t match any of the metals in Study 1 or 2, so repeating these with the same metals would not be helpful to you. According to the passage, color and the time to produce color are both important identifying features of a metal, so in order to identify what metal U4 is, you should replicate both studies with new metals, as in (H). (F) and (G) are incorrect because it’s possible that another metal (not U4) could show similar results to U4 in one respect but not the other, so if you did only one of these studies, you’d mistakenly identify U4 as that metal.


The Correct Answer is (D) — The clamp used in all the Studies in this passage held the metal strips being tested, so it was exposed to the flames as much as the metal strips were. If the clamp were made of copper, then the flame would cause a copper-like reaction regardless of what metal strip was being tested. Therefore, the students would most likely conclude that copper was present in all of the unknown metals, or (D). (C) is the exact opposite, so it is incorrect. The presence of a copper clamp would not affect whether or not the flame reached the clamp, so (B) is incorrect—you may have chosen this answer if you were making an educated guess, because it’s the only answer that includes the keyword “clamp.” Similarly, the presence of copper wouldn’t change the intensity of the flame, so (A) is also incorrect.


The Correct Answer is (J) — You should know that a dependent variable is one that is measured. A dependent variable is not directly controlled by experimenters, but instead is affected by the independent variable, which experimenters manipulate. The color varied depending on the metal used, so the color is the dependent variable. The students chose the mass and type of metals, so (F) and (G) are incorrect. The students may not have precisely controlled temperature, but they made an attempt to keep it constant (in the form of flame intensity), and certainly didn’t measure temperature as an effect of another variable, so (H) is incorrect as well.


The Correct Answer is (A) — This question basically asks you why students conducted Study 2. The results show that some of the unknown metals produced different colors at different times, so measurements of when certain colors appear for different metals can help students identify unknown metals, which is the stated goal of Study 3. (B) is incorrect because the students already know the compositions of the metals in Study 2. (C) is incorrect because the colors don’t appear at a constant time, and the students aren’t trying to make this happen. (D) is incorrect because Study 2 doesn’t indicate which colors appeared, so it was not designed to ensure the colors were the same.