In the following question, select the one word that best substitutes the given phrase: “A period of interval between two regimes or governments.”

Introduction / Context:
This one word substitution question focuses on a political term. The phrase “a period of interval between two regimes or governments” describes a specific situation in governance, often involving a transition of power. The correct word captures the idea of this gap when there is no firmly established ruling authority.

Given Data / Assumptions:

• The phrase refers to a time interval between the end of one government and the beginning of another.
• Interregnum is a political term for a period when normal government is suspended, especially between successive reigns or regimes.
• Polygonum is a botanical term for a plant genus.
• Magnum means great in Latin and is often used in phrases like Magnum opus.
• Presternum refers to part of the sternum in anatomy.
• Only one term connects directly to government and time gaps.

Concept / Approach:
The core concept is a gap in governance. The prefix inter means between, and the root regnum refers to reign or rule. So Interregnum literally means between reigns. Recognising Latin roots is helpful here. The other options belong to unrelated domains: botany, general Latin adjectives and human anatomy. By matching the political context of the phrase with this root analysis, the correct answer stands out.

Step-by-Step Solution:
Step 1: Interpret the phrase carefully as a time when one government has ended and the next has not yet fully begun. Step 2: Consider Interregnum. It is defined as a period when normal government is suspended, especially between successive reigns or political regimes. Step 3: Evaluate Polygonum. This is a plant genus that includes knotweeds and is unrelated to politics or time intervals. Step 4: Evaluate Magnum. While it means great, it does not denote any interval or government context. Step 5: Evaluate Presternum. This is part of the breastbone, not a political term. Step 6: Since only Interregnum accurately describes the interval between reigns or governments, it is the correct answer.

Verification / Alternative check:
Use the word in a sentence: “The country passed through a chaotic interregnum before the new constitution came into force.” This sentence clearly portrays a gap in governance. Substituting Polygonum, Magnum or Presternum would make no sense at all. Dictionaries confirm that Interregnum is a standard term in political history and constitutional law for such intervals.

Why Other Options Are Wrong:
Polygonum is botanical, Magnum is a general descriptor meaning large or great, and Presternum is anatomical. None of these words involve political rule or time gaps. Using them for the phrase given would misrepresent the intended meaning and confuse the reader.

Common Pitfalls:
Because the word Interregnum looks long and somewhat complex, students may doubt it and look for a simpler choice. However, exam questions in general knowledge and English often use classical Latin terms in precisely this way. A helpful memory trick is to link the reg in Interregnum with reign or regime, reinforcing the connection to government rule.

Final Answer:
The correct one word substitute for “a period of interval between two regimes or governments” is Interregnum, so the correct answer is option Interregnum.