Which of the following functions is 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):}

Which of the following functions is not injective ?

Which of the following function is surjective but not injective?

Which of the following function is surjective but not injective?