Updated 2026-08-23intermediate

TOEFL Reading Practice #014 — Same Atom, Two Extremes

Free TOEFL Reading practice: Same Atom, Two Extremes. 11 questions with a full passage and answer key.

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How to use this practice: Read the passage once without a dictionary, then answer the questions on your own. Tap “Answer” under each question to reveal just the correct letter — no explanations, so you can keep testing yourself.
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Passage

Read the full passage. Bracketed letters like [A] mark the four positions for the insert-text question.

Same Atom, Two Extremes

¶1 Carbon is a single element, yet it can appear in two strikingly different forms. Diamond, one of the hardest materials known, and graphite, soft enough to leave a mark on paper, are both made of nothing but carbon atoms. Chemists call these two forms allotropes: different structural arrangements of the same element that end up with very different properties. What separates diamond from the graphite inside a pencil is not the atoms themselves, but how those atoms connect to each other.

¶2 In diamond, each carbon atom bonds tightly to four neighboring atoms, and those bonds stretch out in every direction to form a rigid three-dimensional network. Because every atom is locked into this framework with no weak points, diamond ranks 10 on the Mohs hardness scale, the highest score a mineral can earn. That extreme hardness makes diamond useful for far more than jewelry. Industrial drills and saws are often tipped with diamond, since almost nothing else can cut through rock or metal without wearing down first. The same rigid structure also bends light in a particular way, which is part of why a well-cut diamond sparkles.

¶3 Graphite forms a very different kind of network. [A] Each carbon atom bonds to only three neighbors instead of four, and the atoms arrange themselves into flat sheets shaped like a honeycomb. [B] Between one sheet and the next, however, the bonds are weak, and the sheets can slide across each other with very little resistance. [C] This is exactly why pencils use graphite instead of diamond: as a pencil moves across paper, thin layers slip off and stick to the page. [D] The loosely held electrons between the layers can also move freely, which lets graphite conduct electricity in a way that diamond, with every electron locked into a rigid bond, cannot.

¶4 Diamond and graphite also form under very different conditions underground. Diamond crystallizes only deep within Earth's mantle, at depths of roughly 150 kilometers. There, pressure and temperature are extreme enough to force carbon atoms into that tightly bonded network. Graphite, in contrast, can form much closer to the surface, under far milder conditions. Scientists have used this knowledge to recreate diamond's high-pressure environment in laboratories, growing synthetic diamonds that are chemically identical to natural ones. The lesson extends beyond carbon: how atoms are arranged can matter just as much as which atoms are present in the first place.

  • Mohs hardness scale: a 1-to-10 scale used to compare how easily minerals can be scratched, with 10 being the hardest
  • mantle: the very hot layer of rock between Earth's crust and its core
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Questions

11 questions — every TOEFL Reading question type, in test order.

Q1 · Vocabulary
The word resistance in paragraph 3 ("the sheets can slide across each other with very little resistance") is closest in meaning to
  1. A. speed
  2. B. friction
  3. C. assistance
  4. D. persistence
Answer
Correct: B
Q2 · Reference
The word these in paragraph 1 ("Chemists call these two forms allotropes: different structural arrangements of the same element that end up with very different properties.") refers to
  1. A. diamond and graphite
  2. B. carbon atoms
  3. C. hardness and softness
  4. D. elements and minerals
Answer
Correct: A
Q3 · Essential Term
Based on the information in the passage, the term allotrope can best be explained as
  1. A. any mineral that is mined for industrial or decorative use
  2. B. the extreme hardness that some forms of carbon can have
  3. C. different structural arrangements of the same element that produce very different physical properties
  4. D. the rigid three-dimensional network formed when carbon atoms bond to four neighbors
Answer
Correct: C
Q4 · Factual Information
According to paragraph 2, why are industrial drills and saws often tipped with diamond?
  1. A. Diamond conducts heat away from the blade fast enough to prevent overheating
  2. B. Diamond is cheaper to produce than the metals used for typical drill tips
  3. C. Diamond is more attractive for use in jewelry than any other mineral
  4. D. Diamond is harder than almost anything else, so it does not wear down while cutting through rock or metal
Answer
Correct: D
Q5 · Negative Fact
According to paragraph 3, all of the following are true of graphite EXCEPT
  1. A. Each carbon atom bonds to only three neighbors, forming flat sheets shaped like a honeycomb
  2. B. Each carbon atom bonds to four neighboring atoms in a rigid three-dimensional network
  3. C. The bonds between one layer and the next are weak enough that the layers can slide across each other
  4. D. The electrons between the layers are loosely held and can move freely, allowing graphite to conduct electricity
Answer
Correct: B
Q6 · Sentence Simplification
Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 3? Incorrect choices change the meaning in important ways or leave out essential information.

Highlighted: "The loosely held electrons between the layers can also move freely, which lets graphite conduct electricity in a way that diamond, with every electron locked into a rigid bond, cannot."
  1. A. Graphite conducts electricity because the electrons between its layers can move freely, but diamond cannot conduct electricity because all of its electrons are fixed in place within rigid bonds.
  2. B. Graphite conducts electricity, while diamond does not.
  3. C. Diamond conducts electricity because its electrons are free to move between layers, while graphite cannot because its electrons are locked in rigid bonds.
  4. D. Graphite conducts electricity only when it is compressed into layers, but diamond can never conduct electricity under any circumstance.
Answer
Correct: A
Q7 · Inference
Based on the information in paragraphs 1 and 4, what can be inferred about a piece of graphite that is subjected to the same extreme pressure and temperature found deep in Earth's mantle?
  1. A. It would remain chemically different from diamond even under identical pressure and temperature conditions
  2. B. It would form flat sheets that stack loosely, exactly as it does at the surface
  3. C. Its carbon atoms could be forced into the tightly bonded three-dimensional network that defines diamond, since the same atoms can form different allotropes depending on how they are arranged
  4. D. It would immediately become useless for any industrial purpose
Answer
Correct: C
Q8 · Rhetorical Purpose
The author mentions that industrial drills and saws are often tipped with diamond in order to
  1. A. list the different tools that contain diamond
  2. B. explain why graphite is used in pencils instead of diamond
  3. C. compare the price of diamond jewelry to the price of industrial tools
  4. D. give a concrete example of how diamond's extreme hardness is put to practical use beyond jewelry
Answer
Correct: D
Q9 · Paragraph Relation
How does paragraph 3 relate to paragraph 2?
  1. A. It restates the same rigid three-dimensional network described in paragraph 2
  2. B. It describes an atomic arrangement opposite to the one in paragraph 2, which produces properties opposite to diamond's
  3. C. It provides more evidence that supports the exact same properties described in paragraph 2
  4. D. It explains how the underground formation conditions described in paragraph 4 apply to diamond
Answer
Correct: B
Q10 · Insert Text
Look at the four squares [■] in paragraph 3 that indicate where the following sentence could be added.

This weak connection between layers is also the reason graphite feels slippery to the touch.

Where would the sentence best fit?
  1. A. Square A
  2. B. Square B
  3. C. Square C
  4. D. Square D
Answer
Correct: C
Q11 · Schematic Table 3 pts
Directions: Complete the table by matching the phrases below to the category they belong to. Two of the answer choices will NOT be used. This question is worth 3 points.

Diamond Graphite

  1. A. Each carbon atom bonds to four neighboring atoms in a rigid three-dimensional network
  2. B. Ranks 10, the highest possible score, on the Mohs hardness scale
  3. C. Is often used to tip industrial drills and saws
  4. D. Each carbon atom bonds to only three neighbors, forming flat sheets that stack loosely on top of each other
  5. E. Conducts electricity because loosely held electrons can move freely between its layers
  6. F. Forms only when carbon combines with oxygen at high temperatures
  7. G. Melts at a lower temperature than most other minerals
Answer
Correct: Diamond: A, B, C · Graphite: D, E