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Difficulty: MediumSequential Steps and Chronology

Read the following instructions for preparing a natural indigo dye vat:

To prepare a natural indigo dye vat, follow these steps:
Initially, heat the water in the vat to exactly 50∘C50^\circ\text{C} to ensure the indigo powder disperses evenly. Previously, the indigo must be thoroughly ground into a fine paste with a small quantity of warm water. Prior to introducing the reducing agent, dissolve the alkaline agent (hydrated lime) and stir the solution gently in a single direction to avoid incorporating oxygen. Subsequently, once the pH stabilizes at 1111, add the sodium hydrosulfite. Let the vat rest undisturbed for 4545 minutes. Finally, once the liquid beneath the surface bronze skin turns a clear amber-yellow, the first fabric immersion can begin.

Based on the instructions, which action must be performed immediately before adding the sodium hydrosulfite?

  1. A
    Allow the vat to rest undisturbed for 4545 minutes.
  2. B
    Heat the water in the vat to exactly 50∘C50^\circ\text{C}.
  3. Dissolve the alkaline agent and stir the mixture gently in one direction.Answer
  4. D
    Immerse the first fabric into the amber-yellow liquid.

Answer

Dissolve the alkaline agent and stir the mixture gently in one direction.
The correct answer is the option indicating that the alkaline agent must be dissolved and the mixture stirred. The passage indicates that before introducing the reducing agent, the alkaline agent must be dissolved and stirred, and subsequently, the sodium hydrosulfite (which is identified as the reducing agent) is added.

Step-by-Step Solution

1
Identify the target action in the question, which is the step immediately preceding the addition of sodium hydrosulfite.
The target step is the one that happens just prior to adding sodium hydrosulfite (the reducing agent).
This establishes the timeline anchor for the chronological analysis.
2
Analyze the temporal markers in the text associated with the reducing agent and sodium hydrosulfite.
The text states that 'Prior to introducing the reducing agent, dissolve the alkaline agent...' and 'Subsequently... add the sodium hydrosulfite.'
This links the chemical terms and chronological order, showing that the dissolving of the alkaline agent and stirring happens directly before the addition of the sodium hydrosulfite.
3
Evaluate the options against this established chronology.
The step involving dissolving the alkaline agent and stirring matches the sequence requirement, while other options are either subsequent steps or much earlier tasks.
This confirms the correct option based on text-based sequencing rules.

Key Concept

Sequential Steps and Chronology
Estimated Time:1m 30s
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Topics

Sequential Steps and Chronology

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