Select the related word from the given alternatives so that the analogy Air : Bird :: Water : ? is correctly completed.

Introduction / Context:
This question is a word analogy that checks understanding of the natural relationship between living beings and their primary medium or habitat. Such analogies are frequently used in aptitude tests to measure how well a learner recognises everyday associations and can map them from one pair to another in a logical way.

Given Data / Assumptions:
First pair: Air : Bird. Second pair: Water : ?. Words refer to common real world meanings. We must find an option that mirrors the same type of relationship.

Concept / Approach:
In the pair Air : Bird, air represents the medium or environment in which the bird moves and lives significantly, especially for flying. The relationship is between a habitat or natural medium and the creature that typically uses it. To complete the analogy, we must identify a creature that uses water as its primary medium for living and moving. This interpretation fits standard reasoning questions better than alternative functional interpretations such as action or purpose.

Step-by-Step Solution:
Step 1: Understand Air : Bird. Birds fly in the air. Air is a natural medium associated closely with birds. Step 2: Identify the relationship. The relation can be expressed as medium to typical living being. Step 3: Apply the same idea to Water : ?. We need a living being for which water is the main natural medium. Step 4: Examine each option. Fish: A fish lives and moves in water as its main habitat. Swim: This is an action and not a living being. Wash: This is an activity using water, not a resident of water. Drink: This is another action, not an organism. Boat: It moves in water but is not a natural living creature. Step 5: Select the most appropriate option. Fish is clearly the word that parallels bird in the first pair.

Verification / Alternative check:
We can rewrite both pairs as short statements: A bird lives and moves in air. A fish lives and moves in water. These sentences share the same structure and emphasise habitat. If we try to use Swim, Wash, Drink, or Boat, the statements do not preserve the same natural parallel. Therefore Fish is the only option that gives a clean, direct analogy in line with typical reasoning patterns.

Why Other Options Are Wrong:
Swim is an action that humans or animals can perform in water; it is not a creature that inhabits water. Wash describes an activity using water to clean something and does not match the role of bird in the first pair. Drink is a verb for consuming water and again fails to provide a habitat based relationship. Boat is a man made object used to travel on water, not a natural living organism analogous to a bird.

Common Pitfalls:
A common mistake is to focus only on association with water and ignore the exact type of relation in the first pair. Many words are related to water, but analogies are strict about the pattern. By checking whether the second word plays the same role in its pair as the second word in the first pair, test takers can avoid confusion. Always try to express the relationship in a sentence and see whether the sentence structure stays parallel.

Final Answer:
The analogy Air : Bird :: Water : ? is correctly completed by Fish.