no
Yes, it is.
Yes.
Directly. Their difference IS the difference between them.
Their count. Two in the first case, one in the second.
No.
There are no consecutive rational numbers. Between any two rational numbers there are an infinity of rational numbers.
Find the arithmetic average of the two rational numbers. It will be a rational number and will be between the two numbers.
There are infinitely many rational numbers between any two rational numbers. And the cardinality of irrational numbers between any two rational numbers is even greater.
There are more irrational numbers between any two rational numbers than there are rational numbers in total.
The question cannot be answered because it is nonsensical. The difference between two rational numbers is very very rarely a whole number.
There are countably infinite (aleph-null) rational numbers between any two rational numbers.