Chapter 12, Problem 6E

Find an integer n that shows that the rings $Z_n$ need not have the followingproperties that the ring of integers has.
a. $a^2=a\text{implies}a=0\text{ or}a=1$ .
b. $ab=0\text{implies}a=0\text{ or}b=0$ .
c.ab=ac and a =0 imply b =c.
Is the n you found prime?