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Difficulty: MediumAuthor's Primary Purpose

When dissimilar metals are immersed in an electrolyte such as seawater, galvanic corrosion rapidly degrades the more chemically active metal. To prevent destructive corrosion on vital steel hulls and bronze propeller shafts, marine vessels utilize sacrificial zinc anodes. Zinc possesses a lower electrochemical potential than steel and bronze, causing it to oxidize preferentially. As the zinc anode corrodes over time, it generates a protective electron flow toward the surrounding cathodic structure, preserving the integrity of the vessel's primary components. Consequently, routine drydock inspections focus heavily on measuring anode depletion rates to ensure continuous corrosion defense.

Which of the following best describes the author's primary purpose in this passage?

  1. A
    to outline the general chemical behavior of all metals immersed in electrolytic solutions
  2. to explain how sacrificial zinc anodes protect vital underwater ship components from galvanic corrosionAnswer
  3. C
    to highlight the chemical oxidation rates of zinc during routine drydock inspections
  4. D
    to persuade shipbuilders to replace bronze propeller shafts with less reactive metals

Answer

to explain how sacrificial zinc anodes protect vital underwater ship components from galvanic corrosion
The passage is an expository technical paragraph explaining the function and electrochemical mechanism of sacrificial zinc anodes in preventing marine galvanic corrosion. The author establishes the problem, details how zinc oxidizes preferentially to protect hulls and shafts, and notes maintenance considerations, all unified under the purpose of explaining how these anodes work.

Step-by-Step Solution

1
Analyze the passage structure and identify the main topic
The passage outlines the issue of galvanic corrosion on ships and details the operational mechanism of sacrificial zinc anodes.
Identifying the central subject that spans across all sentences establishes what the author is writing about.
2
Determine the author's tone and rhetorical objective
The author presents objective, technical facts explaining how a system operates rather than arguing a position, narrating an event, or critiquing a policy.
Distinguishing between expository, persuasive, and descriptive intent reveals why the text was written.
3
Synthesize the core subject with the communicative intent
The overarching goal is to explain the protective function and mechanism of sacrificial zinc anodes.
Connecting the technical subject with the expository purpose defines the author's primary purpose.

Key Concept

Author's Primary Purpose
Estimated Time:1m 0s
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