For a relation to be function, every x value should have its unique image in co-domain. If x is related to more than one y value, then that relation is not a function In 1, as you can see, 1 related to -7 as well as 8. Which means 1 has two images viz. -7 and 8. But for a relation to be function, x should have only one image. Thus, it is not a function. The worst is the 4th one in which -2 has 4 images. Therefore, only relation B is a function.
