In this English grammar error spotting question on comparison and degree, identify which numbered part of the sentence is incorrect: "Rohit is two year (1) junior than Mukesh (2) in the office. (3) No Error (4)".

Introduction / Context:
This question focuses on the correct expression of age difference and comparative relationship in English. The sentence is divided into parts: "Rohit is two year (1) junior than Mukesh (2) in the office. (3) No Error (4)". Candidates must choose which segment contains the error. The tested ideas are the correct preposition after "junior" and the standard way of showing comparative rank or age.

Given Data / Assumptions:

• Part (1): "Rohit is two year"
• Part (2): "junior than Mukesh"
• Part (3): "in the office."
• Part (4): "No Error"
• We assume the sentence describes Rohit as being younger or lower in rank compared to Mukesh at the workplace.

Concept / Approach:
In English, adjectives like "junior", "senior", "inferior", and "superior" are normally followed by the preposition "to", not "than". Thus, the standard phrase is "junior to Mukesh", not "junior than Mukesh". Although part (1) also needs "years" instead of "year" in natural usage, competitive exams usually highlight the more important structural error connected to the targeted word, which here is the preposition after "junior". Therefore, part (2) is treated as the incorrect segment because of "junior than".

Step-by-Step Solution:
Step 1: Read the full sentence: "Rohit is two year junior than Mukesh in the office." Step 2: Focus on the comparative adjective "junior" which expresses relative position or age. Step 3: Recall the rule that "junior", "senior", "inferior", "superior", and "prior" are followed by "to", not "than". Step 4: Note that segment (2) uses "junior than Mukesh", which violates this rule. Step 5: Although "two year" in segment (1) should naturally be "two years", exam questions of this type typically focus on a single highlighted rule linked to the adjective and preposition combination. Step 6: Conclude that segment (2) contains the targeted error, so the correct answer is option "2".

Verification / Alternative check:
Rewrite the sentence correctly: "Rohit is two years junior to Mukesh in the office." This corrected version uses both the proper plural "years" and the correct preposition "to", and it sounds natural. Compare with similar sentences: "She is three years senior to him" and "This model is superior to the old one." In each example, "senior" and "superior" are followed by "to". This confirms that "junior than" is not accepted in standard grammar, verifying that part (2) is indeed wrong.

Why Other Options Are Wrong:
Option (1) "Rohit is two year" contains a number and a noun, and although "year" should usually be "years", exam patterns for this specific item generally highlight the preposition error after "junior" as the main tested concept. Option (3) "in the office." is a correct prepositional phrase of place. Option (4) "No Error" is not acceptable because there is a clear problem with the phrase "junior than Mukesh".

Common Pitfalls:
Learners sometimes treat "junior" and "senior" as ordinary comparative adjectives that can take "than", like "younger than" or "older than". However, in standard English their patterns are different. Remembering the fixed combination "junior to", "senior to", "inferior to", and "superior to" helps avoid these mistakes. Practising several examples that use these adjectives correctly will make the correct preposition feel natural.

Final Answer:
The examined error is in segment (2) "junior than Mukesh". It should be "junior to Mukesh". Therefore, the correct answer is "2".