Classification (numbers – perfect squares): Three numbers are perfect squares; one is not a perfect square. Identify the odd number.

Introduction / Context:
This item checks rapid recognition of perfect squares. Among the given numbers, three are squares of integers, while one is not. Your task is to pick the non-square at a glance using common square values.

Given Data / Assumptions:

• 4 = 2^2.
• 64 = 8^2.
• 225 = 15^2.
• 47 is not an integer square (sqrt(47)≈6.855...).

Concept / Approach:
Recall squares up to at least 20^2 and match. Alternatively, factorize: a perfect square’s prime exponents are all even.

Step-by-Step Solution:

Verification / Alternative check:
Take square roots: only 4, 64, 225 yield integer roots; 47 does not.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing 225 with 250 or 256 (16^2). Remember 15^2=225.

Final Answer:
47