In this English vocabulary question, you must select the option that is closest in meaning to the word "Petrify", which is commonly used to describe turning something into stone or making someone extremely afraid or rigid.

Introduction / Context:
This question checks your knowledge of English synonyms for the word "Petrify". In many exam and reading contexts, "Petrify" can be used literally, to mean turning something into stone, or figuratively, to mean making someone so frightened that they become stiff or unable to move. Understanding this dual sense helps you select the most appropriate synonym from the options given.

Given Data / Assumptions:
- The target word is "Petrify".
- The options are "Adorn", "Calm", "Curious", and "Harden".
- We assume standard English dictionary meanings for all words.
- Only one option should match the core meaning of "Petrify".

Concept / Approach:
To solve synonym questions efficiently, you begin by recalling the central sense of the word. "Petrify" in its basic meaning refers to turning something into stone or making it rigid. In extended usage, it means to terrify someone so much that the person feels frozen. Among the given options, we must choose the word that best captures this idea of becoming rigid or stone-like, either physically or metaphorically.

Step-by-Step Solution:
Step 1: Recall that "Petrify" literally means to turn into stone and figuratively means to make extremely rigid or motionless, often due to fear. Step 2: Examine "Adorn". This means to decorate or beautify something and is not related to hardness or fear. Step 3: Examine "Calm". This means to soothe, quieten, or reduce agitation, which is opposite of causing intense fear. Step 4: Examine "Curious". This describes being eager to know or learn and is unrelated to turning rigid or stone-like. Step 5: Examine "Harden". This means to make something hard, firm, or solid, which fits the idea of turning into stone or becoming rigid.

Verification / Alternative check:
If you consider the literal image of petrification, an object changes from a softer state to a stone-like state. The word "Harden" also expresses the process of becoming hard or firm. Therefore, "Harden" aligns with the core meaning of "Petrify". The other options are about decorating, calming, or curiosity, which do not connect logically with the concept of petrification in either physical or emotional sense.

Why Other Options Are Wrong:
"Adorn" is incorrect because it focuses on decoration and beauty, not hardness. "Calm" is incorrect because it reduces anxiety instead of creating rigid fear. "Curious" is incorrect because it relates to interest and desire to know more, which again has no link to becoming rigid or stone-like. None of these capture the key idea of petrification.

Common Pitfalls:
Students sometimes confuse "Petrify" with "Beautify" or "Modify" just because of the similar sound ending with "ify". This is a dangerous habit because English vocabulary often contains similar-sounding words with completely different meanings. Always focus on the definition and mental image associated with the word, not just its sound or suffix. Reading more example sentences improves long-term retention.

Final Answer:
The word that is most similar in meaning to "Petrify" is Harden.