Wan is to colour as which of the following pairs of adjective and related quality has a similar relationship.

Introduction / Context:
This analogy focuses on adjectives that describe a particular quality of something. Wan is an adjective used to describe a lack of healthy colour, especially in the face or overall appearance. We must choose a pair where the adjective relates to the noun in a similar descriptive way. The question tests nuanced vocabulary and the ability to match subtle meaning relationships.

Given Data / Assumptions:

• First pair: Wan : colour.
• Wan describes something that is pale, sickly or lacking in colour and brightness.
• Options for the second pair: Enigmatic : Puzzle, Pallid : Complexion, Insipid : Flavour, Copulent : Weight.
• We assume standard meanings and correct spellings, with copulent intended to suggest corpulent.

Concept / Approach:
The relationship Wan : colour can be understood as “adjective that describes a weakened or reduced state of the quality named by the noun.” Wan describes colour that is faint or unhealthy. We now look for an adjective that describes a similar weakened or reduced state of the quality mentioned in its pair. Pallid means pale or lacking a healthy complexion, and complexion refers to the natural colour and appearance of the skin on the face. This mirrors the way wan relates to colour. While Insipid : flavour also expresses a negative description, pallid plus complexion is closer in its focus on paleness and skin appearance, staying nearer to the idea of colour and its lack.

Step-by-Step Solution:
Step 1: Interpret the first pair. Wan is an adjective that modifies colour, describing it as pale or washed out. Step 2: Identify in the options a pair where the adjective directly modifies the noun as a physical or sensory quality. Step 3: Pallid is an adjective meaning pale, especially describing skin or complexion, and complexion is the colour and texture of facial skin. Step 4: Compare this with Insipid : flavour. Insipid means lacking flavour, which is similar in form but refers to taste rather than visual colour. Step 5: Choose Pallid : complexion because it parallels both the sense of appearance and the idea of paleness that wan carries.

Verification / Alternative check:
We can try fitting each option into an explanatory sentence. “A wan colour” describes colour that looks pale and unhealthy. “A pallid complexion” describes facial colour that is pale and unhealthy, which is extremely close in meaning and structure. “An insipid flavour” describes food that lacks taste, which is a different sensory dimension. “An enigmatic puzzle” means a puzzle that is mysterious, while “copulent weight” is incorrect usage; corpulent describes a person, not weight itself. Thus, Pallid : complexion forms the best mirror to Wan : colour because both express paleness in visual appearance.

Why Other Options Are Wrong:

• Enigmatic : Puzzle: Enigmatic means mysterious; while it can describe a puzzle, the relationship is not about reduction of a quality but about complexity.
• Insipid : Flavour: Although this pair shows adjective describing lack of taste, it concerns a different sense. It is acceptable but less parallel to wan and colour focused on paleness.
• Copulent : Weight: The adjective is incorrectly used; corpulent describes a person as very fat, not weight as a quality, so the pair is mismatched.

Common Pitfalls:
Candidates may be attracted to Insipid : flavour because insipid means lacking flavour, similar to colour that lacks brightness. However, the first pair deals specifically with visual paleness and the health of appearance, and pallid plus complexion matches that nuance more closely. Another trap is to ignore incorrect or awkward usage in pairs, such as copulent with weight, which would not be found in standard English. Paying attention to natural collocations helps avoid these errors.

Final Answer:
The best matching pair is Pallid : Complexion, which mirrors the way wan describes pale or unhealthy colour in the original analogy.