Which of the following functions is a surjection?

If co-domain is R, then which of the following functions is not a surjective (onto) function?

Which of the following function is surjective but not injective?

Which of the following function is surjective but not injective?

Which of the following functions are injective and surjective? : f : N rarr N,f(x)=x^2

Which of the following functions are injective and surjective? : f : Z rarr Z,f(x)=x^2

Which of the following functions are injective and surjective? : f : Z rarr Z,f(x)=x^3

Which of the following functions are injective and surjective? : f : N rarr N,f(x)=x^2+x+1

Which of the following functions are injective and surjective? : f : W rarr W, f(n)= {(n+1 if n is even),(n-1 if n is odd):}