One word substitution: What is the legal term for the crime of betraying your own country?

Introduction / Context:
This vocabulary question focuses on political and legal terminology. Many competitive exams include one word substitution items so that candidates can demonstrate precise command of English. The description here clearly refers to a serious political crime against one's own nation, usually involving helping an enemy or acting against national security.

Given Data / Assumptions:
- Description: "The crime of betraying one's country". - Four options: Treason, Frankness, Fidelity, Allegiance. - We must select the word that is used as a legal and political term for this crime.

Concept / Approach:
Treason is the recognised term in English law and politics for betrayal of one's country, especially by trying to overthrow the government or assisting an enemy during war. The other options express honesty, loyalty, or duty, which are almost opposite to betrayal. Therefore, matching the description to the technical term leads directly to "treason".

Step-by-Step Solution:
Step 1: Identify the key idea in the description: betrayal of your own country. Step 2: Recall the definition of "treason" as a crime involving action against the state or sovereign. Step 3: Compare with "frankness", which means openness or honesty in speaking. Step 4: Compare with "fidelity", which means loyalty or faithfulness. Step 5: Compare with "allegiance", which means duty and loyalty to a ruler or state. Step 6: Notice that the last three are positive qualities, not crimes. Only "treason" is a criminal act and matches the description.

Verification / Alternative check:
Think about familiar phrases: "He was charged with treason" or "High treason against the crown". These are always connected to betraying your country. You would never say "He was charged with allegiance" or "She committed fidelity", because those words are not crimes. This clear difference in usage confirms that "treason" is the one word substitution demanded by the question.

Why Other Options Are Wrong:
Frankness refers to speaking openly and honestly, and is usually considered a positive trait, not a crime. Fidelity means loyalty or faithfulness, which is the exact opposite of betraying your country. Allegiance also means loyalty and duty, particularly toward a state or ruler, so it cannot describe betrayal.

Common Pitfalls:
Some learners may misread quickly and confuse "treason" with "reason" or think that "allegiance" sounds more formal and therefore must be the answer. Another issue is not slowing down to see that the description clearly mentions a crime and betrayal, which automatically rules out words associated with loyalty. Always connect the emotional or moral value in the description with the likely word category, such as crime versus virtue.

Final Answer:
The crime of betraying your own country is called treason.