Let A ={1, 2,  3 }, B= {4, 5, 6, 7}and let f = {(1, 4), (2,5), (3,6)} be a function from A to B. Then f is-

one-one 

It is given that A ={1, 2,  3 }, B= {4, 5, 6, 7}

f:A→B is a function defined as f = {(1, 4), (2,5), (3,6)} 

So, f(1) =4, f(2) = 5, f(3) = 6

It is seen that the image of distinct elements of A under f are distinct.

Hence, f is one-one.

But 7 is only element which is not image of any element of A so f is not onto.