A function is a rule which uniquely associates elements of one set A to another set B. An element can either be one to one or many to one.
For a one to one function, it is one input to one output
For a many to one function, more than one input can have the same output
The inputs are the values of x while the outputs are the values of y
If one input has more than one output, then it is not a function
Looking at the given options, table W is a function because no input has more than one output. For the others, a particular input has more than one output
The correct option is table W