The additive inverse of EVERY positive rational number is a negative number.
No. The additive inverse of zero or a negative rational number is not negative.
The number is 7.
Yes, almost half of them have additive inverses which are negative.
The rational numbers form an algebraic structure with respect to addition and this structure is called a group. And it is the property of a group that every element in it has an additive inverse.
The additive inverse of 18 is -18. The additive inverse of any number is the opposite of that number, such that the sum of the original number and the additive inverse is zero.
The answer depends on whether the "opposite" means the multiplicative inverse or the additive inverse.