Solution:
Given that, A: Rational numbers are always closed under division.Statement A is false as is a rational number because it can be written as .
When we divide any rational number by which is also a rational number, then the resultant number is of the form where is any rational number.
So, the resultant is not defined and hence rational numbers are not closed under division
Statement R is true,
Any real number divided by is not defined.
Therefore, A is false and R is true.
Hence, option 4 is correct.