#### Answer

(a) The sphere has symmetry with respect to the xy plane.
(b) The sphere has symmetry with respect to this line.

#### Work Step by Step

We can write the general equation of a sphere:
$(x-a)^2+(y-b)^2+(z-c)^2 = r^2$
where $(a,b,c)$ is the center of the sphere and $r$ is the radius
The equation of the sphere is: $x^2+y^2+z^2 = 25$
The center of the sphere is $(0,0,0)$
(a) A sphere has symmetry with respect to any plane that includes the sphere's center. Since the xy plane includes the point $(0,0,0)$, the sphere has symmetry with respect to the xy plane.
(b) When $n = 1$, the line $(-1,2,3)+n(1,-2,-3)$ passes through the point $(0,0,0)$
A sphere has symmetry with respect to any line that passes through the sphere's center. Since this line passes through the point $(0,0,0)$ which is the sphere's center, the sphere has symmetry with respect to this line.