Understanding the Use of the Word "Desirous"

The question asks us to identify the grammatically correct sentence out of the given options. The core of the question revolves around the correct usage of the adjective "desirous". "Desirous" means having a strong desire or wish for something or to do something.

When "desirous" is used to talk about wanting something or wanting to do something, it is typically followed by the preposition "of". The structure is commonly "desirous of something" or "desirous of doing something".

Analyzing the Sentences with "Desirous"

Let's examine each option to see which one follows the correct grammatical structure involving "desirous" and the preposition that follows it:

1. My son is desirous in joining the Army.
2. My son is desirous on joining the Army.
3. My son is desirous of joining the Army.
4. My son is desirous for joining the Army.

Based on the standard usage of the word "desirous", the correct preposition to follow it is "of". Let's evaluate each option:

• Option 1 uses "in". The phrase "desirous in" is not the standard or correct way to express a desire for something.
• Option 2 uses "on". Similarly, "desirous on" is not the correct prepositional phrase used with "desirous".
• Option 3 uses "of". This matches the correct grammatical structure: "desirous of doing something". In this case, it's "desirous of joining the Army". This sentence correctly uses "desirous".
• Option 4 uses "for". While "for" is used with desire (e.g., "a desire for wealth"), the adjective "desirous" requires "of". So, "desirous for" is incorrect.

Identifying the Correct Sentence Using "Desirous"

Comparing the options to the correct grammatical rule, the sentence that correctly uses the word "desirous" followed by the appropriate preposition is the one using "of".

Therefore, the correct sentence is "My son is desirous of joining the Army." This sentence correctly expresses the son's strong wish or desire to join the Army, using the proper preposition after "desirous". Understanding the correct prepositions like "of" after "desirous" is crucial for accurate English grammar.