(2) is the correct answer.
Because:
(x
2
+y
2
-z
2
+2xy-2yz)+( y
2
+z
2
-x
2
+2yz-2zx)+(z
2
+x
2
-y
2
+2zx-2xy)+(1-x
2
-y
2
-z
2
) = 1