Four pairs of words are given that mostly show opposite meanings (antonyms). Select the pair in which the words are not opposites in meaning and therefore are related differently from the others.

Introduction / Context:
This verbal reasoning problem involves identifying antonym pairs and spotting the one pair that is not an antonym pair. In such classification questions, three options exhibit a common relationship, such as opposite meanings, while one option shows a different relationship, often similar meanings. Your job is to pick the differently related pair, which becomes the odd one out.

Given Data / Assumptions:
The given pairs are: Robust : Weak, Chaos : Peace, Cruel : kind, Sink : Float, Abduct : Kidnap.
The context is standard English vocabulary, as used in competitive examinations.
Three pairs are expected to be clear antonym pairs, with opposite meanings, and one pair will be a synonym pair, with similar meanings.
Spelling differences like small letters and capital letters do not affect the meaning in this question.

Concept / Approach:
First, you should paraphrase each pair in your own words to understand whether the two words are opposite or similar. Robust means strong, chaos refers to disorder, cruel refers to being very harsh or unkind, sink means go down in liquid, and abduct means to take someone away by force. Once you recognise which pairs are opposites and which are similar, the synonym pair will immediately stand out as the odd one.

Step-by-Step Solution:
Step 1: Robust versus weak. Robust means strong, healthy or sturdy. Weak means not strong or lacking strength. These are opposite ideas, so this pair is an antonym pair. Step 2: Chaos versus peace. Chaos stands for complete disorder, confusion or lack of order. Peace means calm, order and the absence of disturbance. These meanings are opposite to each other, so this pair is also an antonym pair. Step 3: Cruel versus kind. Cruel describes someone who enjoys causing pain or is extremely harsh, while kind describes someone who is gentle, caring and considerate. Again, these two words are clear opposites, so this pair is an antonym pair. Step 4: Sink versus float. To sink means to go down below the surface of a liquid due to greater density, whereas to float means to stay on or rise to the surface of the liquid. These actions are opposite, so this is also an antonym pair. Step 5: Abduct versus kidnap. Abduct means to take someone away illegally, often by force. Kidnap has essentially the same meaning, referring to seizing and carrying away a person, usually to demand ransom or exert pressure. These two words are similar in meaning, so they form a synonym pair, not an antonym pair.

Verification / Alternative check:
You can confirm by trying to replace one word with the other in a sentence. For example, “The criminal planned to abduct the child” can be rewritten as “The criminal planned to kidnap the child” without changing the meaning significantly. However, you cannot replace robust with weak, chaos with peace, cruel with kind or sink with float without reversing the meaning. This replacement test clearly shows which pair is a synonym pair.

Why Other Options Are Wrong:
Robust : Weak – Strong versus not strong; clear opposites, so part of the main antonym group.
Chaos : Peace – Disorder versus calm; another clear pair of antonyms.
Cruel : kind – Harsh versus gentle and caring; again clearly opposite in meaning.
Sink : Float – Going down versus staying or rising up on the surface; opposite actions in a physical sense.

Common Pitfalls:
Some candidates quickly recognise only one or two antonym pairs and may get confused by the presence of a synonym pair. Remember that exam setters often include one synonym pair among antonym pairs. Always check whether the words are truly opposite or merely associated. If they can be used in similar contexts without reversing the meaning, they are likely synonyms rather than antonyms.

Final Answer:
The only synonym pair among the options, and hence the differently related pair, is Abduct : Kidnap.