Classification – Odd one out (charts/shapes vs mathematical constant): Choose the item unlike the others: frequency polygon, Rectangle, Bar, Pi.

Introduction / Context:
Data display terms and shapes contrast with numerical constants. Three entries are graphical/shape concepts; one is a fundamental mathematical constant, not a figure.

Given Data / Assumptions:

• Frequency polygon → statistical chart.
• Bar → chart element/shape.
• Rectangle → geometric shape (form of bar).
• Pi → constant (~3.14159).

Concept / Approach:
Group “graph/shape” vs “numeric constant.” Select the constant as the outlier.

Step-by-Step Solution:
Frequency polygon, Bar, Rectangle → diagrammatic.Pi → numeric constant.

Verification / Alternative check:
Even when used in circle geometry, π remains a number, not a diagram.

Why Other Options Are Wrong:

• The other three are visual/shape-related notions.

Common Pitfalls:
Equating concepts used together (π with circles) with category identity.

Final Answer:
Pi