In this English error spotting question, identify the part of the sentence that contains an error in: "He was smiling, (A) but his eyes retained (B) a look of solemness. (C) No error (D)".

Introduction / Context:
This question focuses on vocabulary choice, specifically the correct noun derived from the adjective "solemn". The sentence is: "He was smiling, (A) but his eyes retained (B) a look of solemness. (C) No error (D)". You need to determine which part contains a word that is not standard or natural in formal English and should therefore be treated as an error in an exam context.

Given Data / Assumptions:

• Full sentence: "He was smiling, but his eyes retained a look of solemness."
• Part (A): "He was smiling,"
• Part (B): "but his eyes retained"
• Part (C): "a look of solemness."
• Part (D): "No error"
• The intended meaning is that although he was smiling, his eyes still showed a serious or grave expression.

Concept / Approach:
The adjective "solemn" means serious, grave, or formal in manner or expression. The standard noun form is "solemnity", not "solemness". While "solemnness" does exist, "solemness" is not a recognised standard spelling or form in formal English. In exam settings, such nonstandard or incorrect derivations are treated as vocabulary errors. The natural phrase would be "a look of solemnity" or "a look of seriousness". Therefore, part (C) contains the incorrect word form and must be marked as the error.

Step-by-Step Solution:
Step 1: Read the sentence and understand the contrast: smiling mouth versus serious eyes.Step 2: Focus on part (C): "a look of solemness."Step 3: Recall that the correct noun derived from "solemn" is "solemnity".Step 4: Replace "solemness" with the correct noun: "a look of solemnity".Step 5: Confirm that parts (A) and (B) are grammatically correct and express a proper contrast between actions and facial expressions.

Verification / Alternative check:
With the correction, the sentence reads: "He was smiling, but his eyes retained a look of solemnity." This is both natural and idiomatic in standard English. We can also compare similar constructions: "a look of sadness", "a look of anger", "a look of calmness", and "a look of solemnity." All use correct noun forms. The abnormal spelling "solemness" does not appear in reputable dictionaries and would be considered wrong in a formal exam.

Why Other Options Are Wrong:

• Option A (part A "He was smiling,") is grammatically correct and appropriately punctuated with a comma before "but".
• Option B (part B "but his eyes retained") is also correct and smoothly links to what is being retained: "a look of solemnity".
• Option D (No error) cannot be selected because the incorrect noun form in part (C) clearly needs correction.

Common Pitfalls:
Many learners try to guess noun forms by simply adding "-ness" to adjectives. While this works for many words (happy → happiness, sad → sadness, dark → darkness), it is not universally correct. Some adjectives have irregular or special noun forms, such as "widow" from "widowed", "strength" from "strong", and "solemnity" from "solemn". Relying only on the "-ness" rule can therefore lead to mistakes like "solemness". It is important to learn the most common irregular derivations for exam purposes.

Final Answer:
The error is in part C; the correct expression should be "a look of solemnity" instead of "a look of solemness".