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Difficulty: MediumLogical Inferences

In agricultural chemistry, researchers analyze how soil moisture affects the decomposition of synthetic urea fertilizers, which release ammonia gas (NH3NH_3). In a controlled experiment, chemist Dr. Hiroshi Sato observed that in dry soils with less than 10%10\% moisture content, urea decomposition was extremely slow, resulting in minimal NH3NH_3 emissions. However, when soil moisture was increased to 30%30\%, NH3NH_3 emissions rose sharply. Interestingly, in soils saturated with water (100%100\% moisture content), NH3NH_3 emissions fell back to near-zero levels, even though the urea had completely decomposed. Sato noted that water-saturated soils trap dissolved ammonia as ammonium ions (NH4+NH_4^+) in solution, preventing it from escaping as gas. Which choice most logically completes the text?

  1. A
    soil moisture is the single most critical variable in determining the overall environmental safety of synthetic fertilizers.
  2. high soil moisture levels can promote the breakdown of urea while preventing the resulting ammonia from being released into the air.Answer
  3. C
    increasing soil moisture beyond 30%30\% will eventually lead to soil toxicity due to the excessive accumulation of ammonium ions.
  4. D
    synthetic urea fertilizers undergo complete decomposition more rapidly in soils with 10%10\% moisture than in water-saturated soils.

Answer

The correct answer is the option stating that high soil moisture levels can promote the breakdown of urea while preventing the resulting ammonia from being released into the air.
The correct option logically completes the text because it directly synthesizes the facts presented. The text states that in water-saturated soil (high moisture), the urea decomposes completely, yet the resulting ammonia is trapped in solution as ammonium ions, which prevents the gas from escaping into the atmosphere. Therefore, high soil moisture can facilitate decomposition while restricting the emission of the resulting gas.

Step-by-Step Solution

1
Analyze the premises regarding soil moisture levels under 10%10\% and at 30%30\%.
Under 10%10\% moisture, urea decomposition is extremely slow, leading to minimal ammonia gas (NH3NH_3) emissions. At 30%30\% moisture, emissions rise sharply.
To establish the initial relationship between low-to-moderate moisture and fertilizer decomposition/emission.
2
Analyze the premises regarding water-saturated soils (100%100\% moisture).
In saturated soils, the urea is completely decomposed, but emissions of NH3NH_3 are near-zero because the ammonia is trapped as ammonium ions (NH4+NH_4^+) in the solution.
To understand the behavior of the system under high moisture and identify why the expected emissions did not occur despite complete decomposition.
3
Synthesize these findings to identify the most logical conclusion.
High soil moisture (saturation) allows the urea to decompose completely, but prevents the resulting ammonia gas from escaping into the atmosphere.
To select the conclusion that directly follows from the premises without introducing external assumptions.

Key Concept

Logical Inferences
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Logical Inferences

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