5

Set 4: Words in Context (Intermediate)

Explanation

Answer: B

PASSAGE

The chemical reaction is highly ______; it proceeds quickly and releases a large amount of heat, posing a risk if not carefully controlled.

Which choice completes the text with the most logical and precise word or phrase?

A. inert
B. volatile✓ Correct
C. gradual
D. silent

Detailed Explanation

A reaction that happens quickly, releases heat, and risks danger is 'volatile'. Volatile refers to a substance that changes easily or a situation that can change rapidly and unpredictably.

Key Evidence:

• "proceeds quickly"

• "releases ... heat"

• "posing a risk"

Why others are wrong: A (Inert means chemically inactive.), C (Gradual means slow.), D (Silent refers to sound.).

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