A = {a, b, c} and B = {x, y, z}, then the function f(a) = y, f(c) = x defines a?

Not a function

One-one and onto function

One-to-one function

None of these

A function must assign each element of A a unique value in B, but f(b) is not defined, so it fails to be a function.

Since not all elements of A have an image in B, it does not satisfy the definition of a function.