Yes.
It is always rational.
Always true. (Never forget that whole numbers are rational numbers too - use a denominator of 1 yielding an improper fraction of the form of all rational numbers namely a/b.)
Never.
No - the sum of any two rational numbers is still rational:
Such a sum is always rational.
They are always rational.
Yes.
It is a rational number.
Since the sum of two rational numbers is rational, the answer will be the same as for the sum of an irrational and a single rational number. It is always irrational.
No, it is always true
It is always rational.
It's always another rational number.
Yes, the set of rational numbers is closed under addition.
The sum of two rational numbers is rational.From there, it follows that the sum of a finite set of rational numbers is also rational.
No
It is always an irrational number.