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 numbers 43 and 54
Addition: 43 + 54 = 3112
Subtraction: 43 - 54 = 112
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 one of the rational numbers, division by 0 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.