The GCF will, yes.
The GCF is, yes.
No, their GCF is always odd.
Yes.Yes.2 can never be a factor of an odd number and because of that it can't be a common factor of any number pair where at least one of numbers is odd.
The GCF of any two odd numbers is always odd. The GCF of any two even numbers is always even. The GCF of an odd and an even number is always odd.
Not sure what the GFC is but if you meant GCF, the answer is no, it is never even.
Any set of odd numbers, yes.
The GCF of any set of odd numbers is odd because odd numbers don't have any even factors.
The GCF of any two odd numbers is always odd because odd numbers don't have any even factors. The GCF of any two even numbers is always even because even numbers are divisible by two and any common factors would have at least one two in common. The GCF of an even and an odd number is odd because odd numbers don't have any even factors.
All of the odd numbers.
The sum of two odd numbers is always even; the sum of three odd numbers is always odd; the sum of four odd numbers is always even; the sum of five odd numbers is always odd; etc
No, it is not true: it depends on what your numbers are.
No - adding an odd quantity of odd numbers will always result in an odd number.