q must be positive in F.
F. r squared will be positive, because any number times itself is positive, and to get a positive number for the answer, the two numbers you multiply need to be the same sign. If r squared is positive, q must be too.
G. q does not have to be positive. If r is a negative number, then q can be negative. Say q=-2 and r=-3. -2-(-3) changes to -2+3, which equals 1.
H. Again, q can be negative if r is negative (two negative numbers multiplied together equals a positive answer.
J. q can be negative because even a negative number turns positive when squared.
Hope this helped you. :)
