The sum of two rational numbers is always a rational number. Which of the following property is illustrated by the given statement?
When you combine (/perform an operation) on any two elements of a set, if the result is also included in the same set then that set is said to be closed under that operation. This is know as Closure Property.
When any two rational numbers are added, the sum will always be a rational number.
Hence, rational numbers are said to be closed under addition.