http://pastpapers.papacambridge.com/view.php?id=Cambridge%20International%20Examinations%20%28CIE%29/AS%20and%20A%20Level/Chemistry%20%289701%29/2016%20Jun/9701_s16_qp_42.pdf
For Q.4(a)(iii) the complex given does not show cis-trans. The
marking scheme says that its mirror images are
superimposable. But how ? I think the mirror images are
non-superimposable. when we say non-superimposable we say
with reespect to 3 -dimensional arrangement. In 3-dimensional they
would be different.
The mirror image is indeed superimposable onto the molecule itself.
Imagine the mirror image, then rotate the mirror image 180 degrees.
It becomes the molecule itself, ie. superimposable.