Logical ReasoningDifficulty: Medium

PT158 S3 Q10 Explanation

Radioactive elements may have been created

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsMain Conclusion

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Stimulus

Radioactive elements may have been created when the universe began. However, even if this occurred, these elements are clearly still being created in the universe today. Radioactive elements are unstable, so most of them decay within at most a few million years into other, nonradioactive elements. So, if no new radioactive elements in the universe today, but there is an abundance of such elements.

What this question is testing

Main Conclusion

Conclusion

The universe is still cranking out radioactive elements right now, today, as we speak.

Evidence

The logic is elegant: radioactive elements have short shelf lives (cosmically speaking — a few million years). The universe is billions of years old. If nobody was restocking the supply, the shelves would be empty. But the shelves are full. Therefore, someone — or something — is still making them.

Evaluate

This is a Main Conclusion question, so watch for the standard traps. The conclusion is stated early ("clearly still being created") and everything else supports it. The last sentence is particularly dangerous — it sounds like a conclusion because it is the final statement, but it is actually just the final piece of evidence. The real conclusion was already declared upfront.

Goal

Grab the main conclusion, not the evidence supporting it or the intermediate reasoning steps.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
10.

Which one of the following most accurately expresses the main conclusion of

Answer choices

  1. Unstated Inference2% picked this

    Any radioactive elements created when the universe began have probably decayed into

    While this statement is probably true based on the argument's premises, it is never stated in the stimulus and is not the argument's main conclusion. The argument's conclusion is that radioactive elements are currently being created. The idea that any original radioactive elements have "probably decayed" is an inference one might draw from the premises, but the argument itself does not make this specific claim. The main conclusion is about ongoing creation, not about the fate of the original elements. Additionally, as an unstated inference rather than a direct claim in the argument, this cannot be the main conclusion by definition — the main conclusion must be something the argument actually asserts.

  2. Correct80% picked this

    Radioactive elements are being created in the

    Why this is right

    This is the argument's main conclusion, stated in the second sentence: "these elements are clearly still being created in the universe today." The word "clearly" signals the author's confident assertion — the claim the argument is designed to prove. Everything that follows serves this conclusion: radioactive elements are unstable (premise), they decay within millions of years (premise), if none were created after the beginning, almost none would remain (intermediate conclusion), but there is an abundance of them (factual observation). The instability, the decay timeline, the counterfactual scenario, and the abundance observation all converge as support for this single claim. This answer captures it accurately: radioactive elements are being created in the universe today.

    Skill tested: Main Conclusion · how this choice captures the argument's function is the move to repeat next time.

  3. Intermediate Conclusion14% picked this

    If no new radioactive elements had been created after the universe began, almost no radioactive elements would be

    This is an intermediate conclusion — a claim that supports the main conclusion while being supported by other premises. It appears near the end of the argument and functions as part of the logical chain: if no new radioactive elements were created, almost none would remain. But this conditional statement, combined with the observation that plenty exist, is the evidence that proves the main conclusion (that new elements are being created). It is also a common "last-claim trap" — appearing at the end of the stimulus, it can be mistaken for the main conclusion simply because of its position. But in this argument, the main conclusion appears earlier, and this statement serves it as a penultimate step in the reasoning chain. The test is always: does this claim support something else, or is it the final destination? This claim supports the "clearly still being created" conclusion.

  4. Background3% picked this

    It is possible that radioactive elements were created when the

    The opening statement that radioactive elements "may have been created when the universe began" is background information — it introduces the topic and sets up the argument but is not the argument's conclusion. The word "may" indicates this is a concession or possibility being acknowledged, not an assertive claim. The argument immediately pivots with "however" and "even if this occurred" to state its main conclusion: these elements are clearly still being created today. The background concession establishes what is already known or plausible; the conclusion is the new claim the argument advances beyond that background. This statement is the starting point of the discussion, not its destination.

  5. Premise1% picked this

    Due to their instability, most of the universe's radioactive elements decay within at most a few million years

    This is a factual premise that provides one piece of the evidentiary chain. The instability and decay rate of radioactive elements is presented as a scientific fact that supports the main conclusion. The argument's reasoning goes: elements decay quickly (this premise) -> if no new ones were made, none would remain (intermediate conclusion) -> but many exist (observation) -> therefore new ones are being created (main conclusion). A premise is a building block offered in support of a conclusion; it is not the conclusion itself. This statement is one of the foundation stones, not the structure built on top of them. The fact that it states an important scientific reality does not change its argumentative role as evidence rather than conclusion.

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