The domain is the set of x-values.
The range is the set of y-values.
For it to be a function, it must pass the vertical line test (which states that any vertical line must intersect the graph at no more than one point).
Question 3
Domain: All real numbers
Range: [1,3]
Function: Yes
Question 4
Domain: All real numbers greater than or equal to 2
Range: All real numbers
Function: No