Which of the following relations are reflexive

1) x~y if and only if x-y is a multiple of 10

2) x~y if and only if xy >= 0

3) x~y if and only if x - y is positive

4) x~y if and only if x+y is odd

5) x~y if and only if x+y is positive

I know the definition of reflexixe is xRx but i dont really understand how to apply it

Thanks