Michael S. answered • 14d
B.S. in Chemistry, Indiana University; Organic Chem Teaching Intern
Before the answer, something you should know about this question: as written, four of the five statements are true. Only #4 is false. So if your assignment wants a single letter, the prompt has almost certainly been copied down as "which is true" when it meant "which is false" - and in that case the answer is #4.
Rather than guess at the wording, here is every statement graded, which answers it either way.
1. The setup should have as many constants as possible. TRUE. Every quantity you do not deliberately hold fixed is free to drift and become a rival explanation for whatever you observe. Controlling them is what earns you the right to say your variable caused the change.
2. Decide on multiple values for the independent variable. TRUE. Two points can be joined by a straight line regardless of the real relationship. Several levels are what reveal the shape of the trend and expose curvature or a threshold you would otherwise miss.
3. There should only be one independent variable. TRUE. Change two things at once and a difference in the result cannot be assigned to either one. That is confounding, and careful measurement afterwards does not repair it.
4. The data only includes the dependent variable you planned for. FALSE. This is the odd one out. Restricting yourself to the one quantity you expected to matter means throwing away everything the experiment is trying to tell you. Real runs produce unplanned observations - a temperature that climbed when it should not have, a solution that changed colour, a reading that drifted - and those are frequently the most informative data you collect. Deciding in advance that only your planned measurement counts is how you record a clean-looking dataset from a run that actually went wrong.
5. Include both qualitative and quantitative data if relevant. TRUE. Numbers are not the only evidence. A precipitate, an odour, a colour change carry real information, and they are often what tells you a run failed even though its numbers look reasonable. Note that 5 is essentially the positive statement of what 4 denies, which is a useful clue: when two options in a list contradict each other, one of them is your answer.
That last observation is worth keeping as a test-taking habit. Scan a list like this for a pair that cannot both be right. Here #4 says restrict your data and #5 says broaden it; they cannot both hold, so the false statement is one of those two, and #5 is plainly good practice. You can often find the answer this way before you have finished thinking about the others.
