Being able to count an actual number of objects, match sets, or identify which group has four and which has five describes which concept?

• A. Subitizing
• B. Cardinality
• C. Counting Principles
• D. One-to-One Correspondence

Answer: (D)

One-to-one correspondence is about pairing each object with a unique number or label. When you count, you go through a set and give every item its own distinct count so that no item is skipped or counted twice. That exact pairing lets you know how many objects there are, because you stop after every item has been matched with a number.

This idea also helps when you match sets. If you pair each item from one set with a unique item from another set and you can pair everyone without leftovers, the two sets have the same size. And when you’re identifying which group has four and which has five, you count each group by giving each object its own number; the final count shows the size of that group, making it possible to compare them.

Subitizing lets you recognize small numbers at a glance without counting, which is a faster skill, but the scenario described relies on counting by assigning unique numbers to each object. Cardinality is the term for the size of a set as determined by that counting process, which again depends on having a one-to-one pairing between objects and numbers.