Select the most appropriate one word for the expression given below.

A politically organised community or major territorial unit ruled by a monarch

The correct one-word substitution is (b) Realm.

• Given expression – A politically organised community or major territorial unit ruled by a monarch: This refers to a kingdom or domain under a king/queen.
• Correct answer word – Realm: Realm means a kingdom or territory ruled by a monarch. (Hindi meaning: राज्य / साम्राज्य)
  Example: The king expanded his realm through alliances.

Meanings of all the other given options:

• Compass – An instrument showing direction (दिशा सूचक यंत्र)
• Sovereign – A supreme ruler or authority (सर्वोच्च शासक)
• Avocation – A hobby or secondary occupation (शौक)

So the correct answer is (b)