f:N→N, where f(x)=x−(−1)x . Then f is
one-one and into
many-one and into
one-one and onto
many-one and onto
fx=x--1x
fx = x-1 , if x is even
= x+1 , if x is odd
so it is one one and onto because f1=2 ,f2=1,f3=4, f4=3 .......etc.