A question that asks you to explain an observation tests whether you can connect a result to a possible cause. Read the observation and separate what changed from what stayed the same. For a comparison between two groups, put the difference in a few words. Then ask how a possible cause would affect each group under the changed conditions. A possible cause can concern the same topic and still fail to explain why the result changed.
Hints
- Hint 1
Compare the 12-hour and 2-hour regimens. Separate what changed from what stayed the same.
- Hint 2
The 21% and 46% values describe benefit relative to uncoated steel. Check how each possible cause affects the two types of steel.
- Hint 3
What could happen more often when the samples switch more often, even though their total wet and dry times stay the same?
Step-by-step
Explain the larger relative benefit
Step 1Separate timing from total exposure
The regimens had the same total immersion time and the same total drying time, but switched every 12 hours or every 2 hours. What needs explaining? The coating reduced mass loss by 21% with slower switches and 46% with faster switches, so the cause must depend on transitions rather than total exposure.
- Step 2
Read the benefit as a comparison
What does the coating's benefit measure? The study compared uncoated steel samples with samples covered by an ultrathin water-resistant coating, so each percentage tells us how much less mass coated steel lost relative to uncoated steel. The cause must make frequent switches favor coated steel more, not only change corrosion overall.
- Step 3
Check the direction of each cause
Would the proposed causes explain why more transitions magnified the coating's apparent benefit? Increasing corrosion by the same proportion on both surfaces leaves the percentage benefit unchanged. Microscopic cracks in the coating would reduce protection with frequent switches, while damage that needs at least 6 hours undisturbed would make the coating more helpful during the longer periods. None gives the coating a larger relative benefit with faster switches.
- Step 4
Count the brief drying episodes
The finding that evaporation briefly concentrates saltwater helps explain the result. As water evaporates, the liquid left on uncoated steel gets saltier and briefly causes extra corrosion, while the coating blocks most saltwater. Switching every 2 hours creates more drying starts than switching every 12 hours, so these brief attacks repeat more often despite equal total exposure. More drying starts can make the coating's relative benefit larger. Choice C.