a and b are two rational numbers such that a + b = 0; then :

1. a = b

2. a and b are numerically equal

3. a and b are numerically equal but opposite in sign

4. none of the above

a + b = 0

a = 0 - b

a = -b

a and b are numerically equal but opposite in sign.

Hence, option 3 is the correct option