Compared to that of alumina glass, ________ silica glass atoms are so far apart that they are unable to re-form...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• Compared to that of alumina glass, [?]
• silica glass atoms are so far apart
• that they are unable to re-form bonds
• after being separated.

Understanding the Meaning

• Let's start reading from the beginning: 'Compared to that of alumina glass,'
• This opening phrase sets up a comparison:
  • 'That' is standing in for something about alumina glass
  • Most likely referring to alumina glass's atomic arrangement
  • So we're comparing the atomic arrangement of alumina glass to something
• This is where we have the blank. Let's look at the choices:
  • Choice A: "silica glass is at a significant disadvantage..."
  • Choice B: "silica glass has a more dispersed atomic arrangement..."
  • Choice C: "a significant disadvantage of silica glass is..."
  • Choice D: "silica glass's atomic arrangement is more dispersed..."
• To see what works here, let's read the rest of the sentence and understand what it's saying!
• The sentence continues: 'silica glass atoms are so far apart that they are unable to re-form bonds after being separated.'
  • This is giving us specific information:
  • Silica glass atoms are very far apart from each other
  • They're so far apart that once separated, they can't re-form bonds
  • This is explaining a physical property and its consequence
• Now, what do we notice about the structure here?
  • The opening phrase "Compared to that of alumina glass" creates a comparison:
  • "That" = the atomic arrangement of alumina glass
  • So we're comparing: the atomic arrangement of alumina glass to [something]
• For this comparison to work properly, we need to compare like things to like things:
  • We can't compare "the atomic arrangement" to just "silica glass" (the material itself)
  • We need to compare "the atomic arrangement of alumina glass" to "the atomic arrangement of silica glass"
• Looking at our choices:
  • Choice D says "silica glass's atomic arrangement is more dispersed"
    • This compares: atomic arrangement TO atomic arrangement
    • This maintains parallel structure in the comparison
  • The other choices break this parallelism:
    • Choices A and B compare "silica glass" (the material) to "that of alumina glass" (the arrangement)
    • Choice C compares "a disadvantage" to "that of alumina glass" (the arrangement)
• So we need Choice D: "silica glass's atomic arrangement is more dispersed, resulting in a significant disadvantage:"
• This properly compares the two atomic arrangements, then the rest of the sentence explains specifically how this dispersed arrangement creates a problem (atoms too far apart to re-form bonds).

Grammar Concept Applied

Maintaining Parallel Structure in Comparisons

When you set up a comparison using phrases like "compared to," you must compare equivalent things - the same types of nouns or noun phrases on both sides of the comparison. This is called maintaining parallel structure (or parallelism in grammar terms).

The Pattern:

• Compared to X, Y [rest of sentence]
• X and Y must be the same type of thing

Examples:

• Incorrect: "Compared to the speed of light, sound moves much more slowly"
  • Comparing "the speed of light" to "sound" (not parallel)
• Correct: "Compared to the speed of light, the speed of sound is much slower"
  • Comparing "the speed of light" to "the speed of sound" (parallel)

In this question:

• "Compared to that of alumina glass" = compared to the atomic arrangement of alumina glass
• Must compare to: "silica glass's atomic arrangement" (Choice D)
• NOT to: "silica glass" (the material) or "a disadvantage"

The pronoun "that" stands in for "the atomic arrangement," so you need to explicitly name the corresponding element for silica glass: "silica glass's atomic arrangement."