Rational numbers are not closed under which operation?
When we add, subtract or multiply any two rational numbers, the result will always be a rational number.
For example: Consider two rational number 43 and 54
Multiplication: 43×54 = 53
In division, when we take two rational numbers other than zero, we will get rational number in result. But when we take 0 as denomiantor, it is not defined and hence it doesn't satisfy the condition of closure property. So only in division, rational numbers do not follow the closure property.