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Question

Difficulty: EasyIdentifying Core Claims and Hypotheses

### Acidification of Lake Echo

Lake Echo recently experienced a rapid decrease in pH, indicating acidification. Two scientists propose different hypotheses to explain this phenomenon.

Scientist 1
The acidification of Lake Echo is primarily caused by acid rain resulting from emissions from a nearby coal-burning power plant. Sulfur dioxide gas emitted by the plant reacts with water vapor in the atmosphere to form sulfuric acid, which then falls as precipitation into the lake watershed.

Scientist 2
The acidification of Lake Echo is primarily caused by natural organic acids. The surrounding coniferous forest has deposited large amounts of pine needles onto the forest floor. Heavy seasonal runoff has carried decomposed organic matter, which contains highly acidic humic acids, from the forest soil directly into the lake.

According to Scientist 2, the decrease in the pH of Lake Echo is primarily caused by which of the following?

  1. A
    sulfur dioxide emissions from a nearby power plant reacting with water vapor in the atmosphere
  2. acidic organic compounds derived from decomposed pine needles carried by runoffAnswer
  3. C
    an increase in underwater volcanic activity releasing sulfuric gases directly into the lake
  4. D
    the chemical breakdown of carbonate rocks in the lake basin due to rising temperatures

Answer

acidic organic compounds derived from decomposed pine needles carried by runoff
Scientist 2 explicitly states that the acidification of the lake is caused by natural organic acids, specifically humic acids from decomposed pine needles, which are transported into the lake via seasonal runoff.

Step-by-Step Solution

1
Locate the hypothesis presented by Scientist 2 in the text.
Scientist 2 states that acidification is caused by natural organic acids (humic acids) from decomposed pine needles on the forest floor.
To identify the core claim of Scientist 2, we must look specifically at Scientist 2's description of the source of the acid.
2
Compare Scientist 2's claim with the provided options to find the match.
The option describing acidic organic compounds from decomposed pine needles carried by runoff directly matches Scientist 2's hypothesis.
This confirms the correct option based on the text.

Key Concept

Identifying Core Claims and Hypotheses
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Topics

Identifying Core Claims and Hypotheses

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