In this geometry based classification question, select the odd word from the given alternatives related to sides and measures in plane figures.

Introduction / Context:
This reasoning question is rooted in basic geometry and asks you to select the odd word from the given list. Three of the options are strongly related to the sides of a right angled triangle, while one is a term used in the context of circles. Such classification questions check conceptual clarity about geometric terms rather than calculations.

Given Data / Assumptions:
- The options are Perpendicular, Base, Hypotenuse, and Radius.- All four terms are used in school level geometry.- We assume standard definitions for triangle and circle related terminology.

Concept / Approach:
In a right angled triangle, the three sides are commonly described as base, perpendicular, and hypotenuse. The term radius, however, refers to the distance from the centre of a circle to a point on its circumference. A simple classification is therefore possible: three options belong to the right triangle family, and one belongs to the circle family. The circle related term is the odd one out.

Step-by-Step Solution:
Step 1: Base is the side of a triangle that is usually taken as the reference side for height.Step 2: Perpendicular is the side that forms a right angle with the base in a right angled triangle.Step 3: Hypotenuse is the side opposite the right angle and is the longest side of a right angled triangle.Step 4: Radius is a line segment drawn from the centre of a circle to any point on the circle. It is not a side of a triangle.Step 5: Three of the terms are names for sides of a right angled triangle, while one is not.

Verification / Alternative check:
You can picture a right angled triangle and label its sides. You will easily find base, perpendicular, and hypotenuse, but there is no side called radius. Conversely, drawing a circle immediately suggests the radius but not base or hypotenuse. This visual check confirms the classification.

Why Other Options Are Wrong:
Perpendicular: One of the legs of a right angled triangle.Base: Another side of the triangle used along with the perpendicular.Hypotenuse: The third side of the right angled triangle.

Common Pitfalls:
Students sometimes overcomplicate by thinking about formulae like area or Pythagoras theorem. The question only needs identification of which term belongs to a circle instead of a triangle. Keeping focus on the basic definitions makes the problem easy.

Final Answer:
The odd word is Radius because it is a circle related term, whereas the other three describe sides of a right angled triangle.