A set is countable if its members can be listed or put into one-to-one correspondence with the set of natural numbers. Countable sets include finite sets like the set of even prime numbers less than 10, which contains {2, 3, 5, 7}. A set is countable if you can count its members by assigning each one a unique natural number.

1. Countable Set
• A set is said to be countable, if you can make a list of its
members.
• A set is countable if either it is finite or it can be
made in one to one correspondence with the set of
natural numbers.

2. Example of countable sets
•The set of even prime numbers that
contains only one element.
answer: {2}
•The set of prime numbers less than 10.
answer: {2,3,5,7}.