Sentence improvement (idiomatic expression): choose the best substitute for the underlined part in the sentence below. Mahatma Gandhi is called as the Father of the Nation.

Introduction / Context:
This question tests your familiarity with an extremely common English structure: \"be called\" followed directly by a noun phrase. The sentence is about Mahatma Gandhi and his widely known title \"the Father of the Nation\". Examinations often check whether you know that no preposition is used after \"called\" in such patterns.

Given Data / Assumptions:

• Sentence: Mahatma Gandhi is called as the Father of the Nation.
• The underlined part is \"called as the Father of the Nation\".
• Options adjust how the title is attached to \"is called\".
• The intended meaning is that people give Mahatma Gandhi this honorific title.

Concept / Approach:
In standard English, when we say that someone has a particular name or title, we use the structure \"be called\" plus the name, without any preposition: \"He is called the Father of the Nation.\" The phrase \"called as\" is wrong in this context. The definite article \"the\" is required before \"Father of the Nation\" to mark a unique title.

Step-by-Step Solution:
Step 1: Note the basic pattern: subject + \"is called\" + title. Step 2: Remove \"as\" mentally and see whether the sentence becomes smoother: \"Mahatma Gandhi is called the Father of the Nation\". Step 3: Confirm article usage. Since \"Father of the Nation\" is a unique honorific, it needs \"the\" before it. Step 4: Compare with alternative forms such as \"He is known as the Father of the Nation\", where \"as\" is correctly used because the verb itself is different. Step 5: Select the option that removes \"as\" and keeps the article \"the\" in place.

Verification / Alternative check:
You can test the pattern with other titles: \"She is called the Nightingale of India\", \"He is called the Iron Man of India\". In none of these sentences do we insert \"as\" after \"called\". The phrase \"called as\" is considered incorrect in standard written English when we are talking about a name or title. This confirms that \"called the Father of the Nation\" is the correct structure.

Why Other Options Are Wrong:
Option \"called Father of the Nation\": This removes both \"as\" and \"the\". It is possible in very informal style, but it sounds incomplete because the uniqueness of the title is not clearly marked. Option \"Father of the Nation\": This removes the verb phrase and leaves only the noun phrase, so the sentence would become \"Mahatma Gandhi is Father of the Nation\", which is grammatically weaker than the standard \"is called the Father of the Nation\". Option \"No improvement\": This keeps \"called as\", which is non-standard and incorrect in this structure.

Common Pitfalls:
Learners often confuse \"called\" with \"known as\". The expression \"known as\" correctly takes \"as\" (for example, \"He is known as the Father of the Nation\"), but \"called\" does not. Mixing these patterns leads to the incorrect phrase \"called as\". Remember: \"called\" plus title, but \"known as\" plus title.

Final Answer:
The correct sentence is: Mahatma Gandhi is called the Father of the Nation. So, the correct option is called the Father of the Nation.