Hi -
R = {0} so when I say all x in R, only value x can take is x=0. I said for all x in R just to make it exactly similar to how you define element 1 for any Ring.
if e.x = x.e = x for ALL x in R, then e is unique and is called multiplicative unity (1).
Now in our example R={0), put e=0
0.x = x.0 = x for all in x R.
For any other Ring this is true ONLY if x=0. But as in our special example x=0 is the only element in the Ring we can use for all x in R and hence the definition of 1 is satisfied, thus e=0=1.
I beleive this question is more to do with the understading of definitions than anything else.