Central Board Of Secondary Education [CBSE] — fault in marking scheme of cbse science paper of class x.

My son is appearing class x cbse board examination 2019.in his science paper (Series jsm/4 set-2 code 31/4/2) in question no 13 there is a part of the question “draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prisms.” for this question he has not drawn answer figure given in ncert science book for class x, because this figure is wrong. But he has drawn a different figure which is actually correct. So he must not loose mark. Cbse is adopting faulty system in blindly accepting ncert book's answer. If we apply snell's law then easily we can prove that ncert book's figure is wrong. Very surprising to say that the professors who have written the ncert book, they have not understood snell's law. The cbse marking scheme has accepted the wrong ncert figure many times, also this time. What we can say about cbse education standard? For so many years the students of india are getting mark by drawing the wrong figure. The ncert authors have no standard to write the book, also the persons who have prepared the marking scheme have no standard to do so.