Which option best captures the formal idea of one-to-one correspondence in pairing elements of two sets?

• A. Symmetry
• B. Subset relation
• C. Parallelism
• D. One-to-one correspondence

Answer: (D)

One-to-one correspondence is the idea that elements of two sets are paired so that each element in the first set has a unique partner in the second, and each element in the second set is paired with exactly one element of the first. This creates a perfect mapping between the sets, often called a bijection when both sets are fully matched.

This option names the exact concept of that precise pairing. The other ideas don’t describe this kind of one-to-one matching: symmetry involves mirroring or mutual relation, a subset relation concerns containment of elements, and parallelism refers to items that line up or run alongside each other without guaranteeing a unique, two-way pairing.