## 1.

The Correct Answer is (C) — The question asks you to identify the reason why the scientists exposed some rats to clean air. The pollution of the air is an independent variable in these experiments, as it is being changed by the scientists so they can observe its effect on the dependent variable, which is the number of pregnant rats. The scientists use the trial with clean air as a control---a basis to compare the trials with polluted air. If they hadn’t run a trial with clean air, they would have no way of seeing how the fertility of rats is affected by polluted air. (A) is incorrect because no information is gained about the level of pollutants in clean air. (C) is incorrect because clean air helps determine the effects of polluted air, not proteins. (D) is incorrect because there is no information gained about the chemical structures of the pollutants.

## 2.

The Correct Answer is (H) — The question asks you to identify the correct conclusion based on Table 1. CO-polluted air greatly decreases the fertility of rats with low-protein diets, but it has almost no effect on rats with high-protein diets, which suggests that a high-protein diet has a protective effect on rats. Therefore, (J) is incorrect, as high-protein diets and CO-polluted air resulted in 48 pregnant rats, which is the second highest fertility rate of the four cases tested. (F) and (G) describe two circumstances that decrease the fertility of rats; you can see from the table that CO exposure and low-protein diets lead to fewer pregnancies. Therefore, these options are also incorrect.

## 3.

The Correct Answer is (A) — The question asks you to identify the conditions which lead to the lowest number of pregnant rats based on Table 1 and Table 2. The lowest number of pregnancies, which is 8, occurs with a low-protein diet and SO2 pollution as seen in Table 2. If you chose (B), you may have forgotten to consider Table 2 when answering the question.

## 4.

The Correct Answer is (G) — The question asks you to predict the result of the experiment if it were repeated with ozone, which has a toxicity between CO and SO2, on rats on a low-protein diet. From Table 1, the number of pregnancies in rats with a low-protein diet and CO-polluted air is 18. Table 2 shows that this number is 8 if the air is SO2-polluted instead. The number of pregnancies in an ozone-polluted low-protein diet sample is expected to be somewhere between the two. The only option that matches this scenario is (G). (F) and (H) are incorrect since ozone has a lower pregnancy rate (suggesting a higher toxicity) than SO2, which contradicts the information given in the question. (J) is incorrect as the values for the number of pregnancies in CO-polluted and SO2-polluted environments don’t match Table 1 and Table 2.

## 5.

The Correct Answer is (A) — The question asks you to predict a logical continuation to the studies of the researchers. The researchers are studying the effects of polluted air on the fertility of rats. The only answer option that relates to the fertility of rats in areas affected by air pollution is (A), since heavy automobile traffic causes CO-polluted air as mentioned in the first paragraph. (B) may be tempting since power plants are mentioned in the first paragraph; however, solar power stations are not typical power plants and there is nothing that suggests that they produce SO2. (C) may be tempting since rats are also tested with clean air in the experiment; however, the scientists want to study the effects of pollution, not the effects of the absence of pollution. (D) is incorrect as there is nothing that suggests that the scientists are interested in the effects of heavy precipitation on rat fertility.

## 6.

The Correct Answer is (J) — The question asks you to identify a dependent variable which was common in Experiment 1 and Experiment 2. The number of pregnant rats is dependent on all of the other conditions, and it is the final value measured by the scientists; therefore, it is a dependent variable in both experiments. (F), (G), and (H) were also all measured by the scientists; however, they were controlled in the experiment and are thus independent variables.

## 7.

The Correct Answer is (A) — The question asks you the factor by which exposure to SO2 decreases the number of pregnant rats fed a low-protein diet. From Table 2, among rats on a low-protein diet, there were 31 pregnant rats in the clean-air group and 8 in the SO2-polluted-air group. $\frac{31}{8}\simeq&space;\frac{32}{8}=&space;8$ as many pregnant rats. You may have chosen (C) if you calculated the factor by which CO-polluted air decreases pregnancies in rats on low-protein diets. You may have chosen (B) or (D) if you misinterpreted the question or made a mistake dividing the two numbers.

## 8.

The Correct Answer is (G) — The question asks you to identify the reason why aluminum foil was used to cover the beakers. The foil would prevent water vapour from escaping the beaker, which would otherwise cause the final measurements of volume remaining in the beaker be lower than the real values. (F) is incorrect since maximizing the possibility of contamination will likely be detrimental to the test results, and there is nothing that suggests that aluminum foil would even cause this. (H) is incorrect because aluminum foil would have no effect on the rate of absorption, and this is also not a desirable effect for the researchers. (J) is incorrect since there is nothing in Experiment 1 that relates to the flow rate of water.

## 9.

The Correct Answer is (C) — The question asks you to predict a possible amount for the volume of water that would flow through the granite slab after 78 hours, which is 6 hours after the last data point on Figure 1. The flow through the granite is marked by the crosses on Figure 1. Extending the trend, you can predict that the next cross will be placed between 0.8 and 1.0 mL. You may have chosen (A) or (D) if you looked at the lines for a different type of stone instead of granite. You may have chosen (B) if you underestimated the increase in volume between data points.

## 10.

The Correct Answer is (F) — The question asks you to identify the relationship between the density of rock and the amount of water it is able to absorb. Higher volumes remaining in the beaker suggest that the porosity, or the amount of water the rock absorbs, is lower. Ordered from lowest to highest density, the rocks are Sandstone, Shale, Limestone, Granite, and Basalt. In the same order, the volume of water that remains in the beaker is 87 mL, 89 mL, 90 mL, 93 mL, and 96 mL. These values are ordered from smallest to largest, suggesting Sandstone, has the highest porosity while Basalt has the lowest. Therefore, porosity decreases with increasing density. If you picked (G) or (H), you may have forgotten to arrange the rocks by their densities. If you chose (J), you may have assumed that higher volumes suggested higher porosities.

## 11.

The Correct Answer is (C) — The question asks you to predict the amount of water that would be left in the beaker if a piece of gabbro with a density of 3.03 mg/m3 were added to the beaker. The density of gabbro is higher than any other material tested, suggesting that it would have a lower porosity and higher volume of water left in the beaker compared to the other trials. Therefore, (A) and (B) can be eliminated. (D) is incorrect since the beaker is originally filled with 100 mL of water, making it impossible for it to have 101 mL of water after some amount of it is absorbed.

## 12.

The Correct Answer is (F) — The question asks whether water flows slower through rocks with higher porosity. To answer this question, use Table 1 to find the two rocks which left the lowest volume of water in the beaker (this suggests that they have higher porosity). These two, shale and sandstone, have the highest volumes of flow-through for all amounts of time elapsed as seen in Figure 1. Therefore, water does not flow slower in rocks with higher porosity, eliminating options (H) and (J). (G) is incorrect because shale and sandstone, which absorbed the most amount of water in Experiment 1, allowed water to flow the fastest in Experiment 2.

## 13.

The Correct Answer is (B) — The question asks for the effect of water flowing around the slabs on the results of Figure 1. Water flowing around the slabs would allow some water to go through the experimental setup without having to go through the rocks. This would make the measured value of water flow higher than the actual value, which supports (B) and eliminates (A). (C) is incorrect because the error should affect all the measurements in the same way. (D) is incorrect because the error should give the water an alternative path to flow through, which would change the amount of water that is measured at the end of the experimental setup.

## 14.

The Correct Answer is (H) — The question asks you to estimate the density of an unknown rock that allows 0.8 mL of water to flow through in 72 hours. From Figure 2, the volume of water this rock allows through is between the volumes allowed by granite and limestone, which means that the density of this rock is between the densities of granite and limestone. This eliminates options (F) and (J). A volume of 0.8 mL is closer to the volume allowed through by granite; therefore, the density of the unknown rock should be closer to that of granite than limestone. This eliminates (G), since 2.56 is closer to 2.55 than it is to 2.64.

## 15.

The Correct Answer is (B) — The question asks you to identify the trend in the volume of Argon as temperature increases. Moving down the “Ar” column of Table 1, it can be seen that gas volume consistently increases as temperature increases. You may have chosen (A) if you followed the trend as temperature decreases. (C) and (D) are incorrect since there is a clear, linear trend that can be seen in Table 1.

## 16.

The Correct Answer is (J) — The question asks whether the changes in temperature affect each of the gases equally. Looking at the differences between each row of Table 1, you can see that every 20°C increase in temperature changes the volumes of the gases between 3.2 and 3.7 mL. Small inconsistencies in data are a part of scientific experiments, and scientists extract relevant relationships from imperfect data. Like a scientist, you can conclude that the volumes of gases are affected in the same way by the changes in temperature, eliminating (F) and (G). (H) is incorrect because the differences in the change in volumes are negligible---they are due to random errors in the experiment.

## 17.

The Correct Answer is (D) — The question asks you to identify the best way to calculate the mass of the gas alone based on the mass of the syringe and mass of the gas and syringe together. The mass of the syringe, S, needs to be subtracted from the mass of the syringe and gas together, S + G, to get the mass of the gas , G: (S + G) - S = G.

## 18.

The Correct Answer is (H) — The question asks you to predict the mass of the syringe with 150 mL of Nitrogen gas in it. The mass of the syringe is 100 grams, and subtracting this from the mass of a syringe with 75 mL of nitrogen (from Table 2), you find that 75 mL of Nitrogen weighs 100.06 – 100 = 0.06 g. 150 = 75 × 2, suggesting that 150 mL of nitrogen will weigh 0.06 × 2 = 0.12 g. You need to add the mass of the syringe to the weight of the gas for the final mass: 100 + 0.12 = 100.12 g. You may have chosen (F) if you forgot to add the mass of the nitrogen to the mass of the syringe. If you chose (G) or (J), you may have used a gas other than nitrogen, or if you miscalculated the weight of 150 mL of gas.

## 19.

The Correct Answer is (C) — The question asks you to identify the gas with the lowest mass per unit volume. Taking the measurements of 25 mL of each gas with the syringe, you find that the syringe with CO2 weighs 100.05 g, with O2 weighs 100.03, with N2 weighs 100.02 g, and with Ar weighs 100.04 g. N2 has the lowest mass of the four, therefore nitrogen is the correct answer. If you chose (A), you may have thought that the question was asking which had the highest density.

## 20.

The Correct Answer is (H) — The question asks you to predict the volume of methane at 67°C if 50 mL of methane and the syringe together weigh 100.03 g. The first piece of information about the weight of methane is completely irrelevant since Table 1 shows that all gases have approximately the same volumes at each temperature, despite their varying weights seen in Table 2. Therefore, (F), (G), and (J) are false since they predict that the volume occupied by methane will be different than the other gases since its weight is different. (H) is the only option within the range of volumes of the other gases at the given temperature (56.5 to 57.0 mL)

## 21.

The Correct Answer is (A) — This is a knowledge question, which asks you to order the speed of molecules in the solid, liquid and gas phases of a compound. Since the question says that temperature is a measure of the particles’ energy, you can guess that gas molecules are the fastest because liquids turn into gas when you heat them up. Gas molecules are always faster than liquid molecules since they have higher energies and are further apart. Liquid molecules are slower than gas molecules but faster than solid molecules which are the slowest of the three.