Find the odd geometric figure (polygon vs curved): Choose the one that is not a polygon with straight sides.

Introduction / Context:
Odd-one-out questions in basic geometry usually turn on a single defining property. Here the clean divider is “polygon with straight sides” versus “non-polygon with only curved surface(s).”

Given Data / Assumptions:

• Square: plane polygon with 4 straight sides and 4 right angles.
• Rectangle: plane polygon with 4 straight sides and right angles.
• Circle: plane curve with no straight sides or vertices (non-polygon).
• Sphere: three-dimensional solid; its surface is entirely curved, not a plane polygon.

Concept / Approach:
Classify each option by two criteria: (1) polygon vs non-polygon and (2) 2D vs 3D. A polygon must be a 2D figure with straight line segments as sides. Both circle and sphere fail the “straight sides” test; however, sphere is additionally 3D, which separates it even more strongly from the set.

Step-by-Step Solution:

Verification / Alternative check:
Consider dimensionality alone: sphere is 3D; the others are 2D figures. That single criterion already isolates sphere as the outlier.

Why Other Options Are Wrong:
Square and rectangle are polygons; circle, while not a polygon, is still a 2D figure. Sphere differs in being 3D and non-polygonal simultaneously.

Common Pitfalls:
Do not confuse “circle vs polygon” and miss that sphere adds an extra difference (3D). The strongest single odd choice is the sphere.

Final Answer:
Sphere